Tải bản đầy đủ - 0 (trang)
12b Liver, Gallbladder, and Pancreas Development

12b Liver, Gallbladder, and Pancreas Development

Tải bản đầy đủ - 0trang

805



Chapter Twenty-Six  Digestive System







Ventral

mesentery



Esophagus



Dorsal

mesentery



Gallbladder

(cystic bud)

Liver



Foregut



Cystic bud

Vitelline duct



Lesser curvature

of stomach



Falciform

ligament



Liver buds



Greater curvature

of stomach

Dorsal pancreatic bud

Ventral pancreatic bud



Dorsal

pancreatic bud



Ventral

pancreatic bud



Vitelline duct



Primary intestinal

loop



Midgut

Hindgut



(a) Week 4: Liver, gallbladder, and pancreatic buds develop



(b) Week 5: Greater and lesser curvatures of stomach form



Direction

of stomach

rotation

Falciform ligament



Gallbladder

Falciform

ligament



Esophagus

Liver



Liver



Greater

omentum



Lesser omentum

Gallbladder



Direction

of duodenum

rotation



Ventral pancreatic bud

Direction of pancreas,

bile duct rotation



Stomach



Dorsal

pancreatic bud



(c) Weeks 6–7: Rotation of stomach, pancreatic buds



Common bile duct

Pancreas



Duodenum



(d) Week 8: Postnatal position of organs attained



Figure 26.22

Development of the Digestive System Foregut. (a) The foregut of the digestive system begins to develop from the primitive gut during week 4 of development.

Stages of foregut development continue at (b) week 5, (c) weeks 6–7, and (d) week 8.



Table 26.5



Anatomic Derivatives of the Primitive Gut Tube



Organs Formed



Foregut



Midgut



Hindgut



Digestive organs



Pharynx, esophagus, stomach, proximal

half of duodenum



Distal half of duodenum; jejunum,

ileum, cecum, appendix, ascending

colon, proximal (right) two-thirds of

transverse colon



Distal (left) one-third of transverse

colon; descending colon, sigmoid colon,

rectum, superior portion of anal canal



Accessory digestive organs



Most of liver; gallbladder, biliary

apparatus, pancreas



Non-digestive organs



Lungs, spleen



Urinary bladder epithelium, urethra

epithelium



806



Chapter Twenty-Six  Digestive System



Liver



Ventral

mesentery

Dorsal

mesentery



Vitelline

duct

Stomach



Ventral

mesentery



Descending

abdominal

aorta

Primary intestinal

loop (midgut)



Caudal loop



Dorsal

mesentery



Cranial loop

Caudal loop



Cranial loop



Hindgut

Superior

mesenteric artery



90° counterclockwise

rotation



(a) Week 5: Primary intestinal loop forms



(b) Week 6: Herniation of loop; 90° counterclockwise rotation



Caudal loop

(forms much of large intestine)



Duodenum

Transverse colon



Direction of rotation 180°

counterclockwise



Colon



Vitelline duct



Cranial loop

(forms most of

small intestine)



Small intestine

Ascending

colon



Descending colon



(c) Weeks 10–11: Retraction of intestines back into abdominal cavity;

180° counterclockwise rotation

Cecum



Sigmoid colon

Appendix



Rectum



(d) Postnatal position



Figure 26.23

Development of the Digestive System Midgut. The midgut of the digestive system forms almost all of the small intestine and the proximal region of the large

intestine. Development of these structures is shown at (a) week 5, (b) week 6, and (c) weeks 10–11. (d) The postnatal position of the digestive organs.



Clinical Terms

bariatric surgery (gastric bypass)  Surgically narrowing or blocking off



a large portion of the stomach; typically performed in severely

obese people who have had trouble losing weight by more

traditional methods.

colostomy  A surgical procedure that moves and attaches a portion

of the colon so it exits through the abdominal wall. Materials

moving through the large intestine drain into a bag (ostomy

pouch) attached to the abdomen.

dysentery  (dis-en-tēr-ē; dys = bad, entera = bowels)  Painful, bloody

diarrhea due to an infectious agent.

gastroenteritis  (gas′trō-en-ter-ı ′̄ tis)  Inflammation and irritation of the

GI tract, often associated with vomiting and diarrhea.

hemorrhoids  (hem′ŏ-roydz; rhoia = flow)  Dilated, tortuous veins

around the rectum and/or anus.



intussusception  (in-tŭs-sŭ-sep′shŭn; intus = within, suscipio = to



take up)  Type of intestinal obstruction in which one part of

the intestine constricts and gets pulled into the immediately

distal segment of intestine; most commonly seen near the

ileocecal junction. Symptoms include bloody stools and severe

abdominal pain.

mumps  (a lump)  Viral infection of the parotid glands, resulting in

painful swelling of the glands.

volvulus  Twisting or torsion of an intestinal segment around itself. If

left untreated, obstruction of digestive materials results, and the

segment necroses due to poor blood supply. Symptoms include

intense abdominal pain and vomiting.



807



Chapter Twenty-Six  Digestive System







Chapter Summary

26.1 General

Structure and

Functions of the

Digestive System



26.2 Oral Cavity











The digestive system breaks down ingested food into usable nutrients.











The digestive organs are the oral cavity, pharynx, esophagus, stomach, small intestine, and large intestine. The accessory digestive

organs are the teeth, tongue, salivary glands, liver, gallbladder, and pancreas.



26.1a Digestive System Functions









Mechanical digestion is the physical breakdown of ingested materials, and chemical digestion is the enzymatic breakdown of

molecules.











Motility moves materials through the GI tract. Peristalsis moves materials from the mouth toward the anus; mixing blends ingested

materials.











Secretion is the production and release of fluids; absorption is the movement or transport of materials across the wall of the GI

tract.











The oral cavity is the entryway into the GI tract.



26.2a Cheeks, Lips, and Palate









The cheeks form the lateral walls of the oral cavity, and the lips frame the anterior opening formed by the orbicularis oris muscle.











The palate is the oral cavity roof: The hard palate is the anterior, bony portion, and the soft palate is the posterior, muscular

portion.



26.2b Tongue









The tongue moves and mixes ingested materials; its dorsal surface has papillae.



26.2c Salivary Glands









Saliva is a fluid secreted primarily by three pairs of multicellular salivary glands, called extrinsic salivary glands. It moistens food

and provides lubrication.



26.2d Teeth









Adults have 32 permanent teeth of four types: incisors, canines, premolars, and molars.



26.3 Pharynx











Pharyngeal constrictors contract sequentially during swallowing.



26.4 General

Arrangement of

Abdominal GI Organs



26.4a Peritoneum, Peritoneal Cavity, and Mesentery









Parietal peritoneum lines the internal body wall; visceral peritoneum covers abdominal organs.











Intraperitoneal organs are completely surrounded by visceral peritoneum; retroperitoneal organs are only partially ensheathed.











Mesenteries are double layers of peritoneum.



26.4b General Histology of GI Organs (Esophagus to Large Intestine)









The mucosa is composed of epithelium, an underlying lamina propria, and the muscularis mucosae.











The submucosa is a dense irregular connective tissue layer containing blood vessels, lymph vessels, and nerves.











The muscularis usually has two smooth muscle layers: an inner circular layer and an outer longitudinal layer.











The adventitia is the outermost covering; when covered by visceral peritoneum, it is called a serosa.



26.4c Blood Vessels, Lymphatic Structures, and Nerve Supply





26.5 Esophagus







GI tract organs have extensive blood vessels, lymphatic structures, and nerves.



26.5a Gross Anatomy









The esophagus conducts swallowed materials from the pharynx to the stomach.



26.5b Histology









The esophagus is lined by nonkeratinized stratified squamous epithelium.











The muscularis has all skeletal fibers superiorly, changes to intermingled skeletal and smooth fibers in the middle, and contains all

smooth fibers inferiorly.



26.6 The Swallowing

Process











Swallowing has three phases: The voluntary phase moves a bolus into the pharynx; the pharyngeal phase moves the bolus through

the pharynx into the esophagus; and the esophageal phase conducts the bolus to the stomach.



26.7 Stomach



26.7a Gross Anatomy









Mechanical digestion and chemical digestion occur in the stomach.











The four stomach regions are the cardia, fundus, body, and pylorus.



26.7b Histology









The stomach mucosa is composed of a simple columnar epithelium containing gastric pits and gastric glands.











The muscularis has three smooth muscle layers: inner oblique, middle circular, and outer longitudinal.



26.7c Gastric Secretions









Five types of secretory cells form the gastric glands: surface mucous cells (secrete mucin), mucous neck cells (secrete acidic

mucin), parietal cells (secrete hydrochloric acid and intrinsic factor), chief cells (secrete pepsinogen), and enteroendocrine cells

(secrete gastrin and other hormones).

(continued on next page)



808



Chapter Twenty-Six  Digestive System



Chapter Summary (continued)

26.8 Small Intestine



26.8a Gross Anatomy and Regions









The small intestine finishes chemical digestion and absorbs most of the nutrients.











The small intestine is divided into the duodenum, jejunum, and ileum.



26.8b Histology





26.9 Large Intestine







The small intestine has circular folds with fingerlike villi projecting from them. The villi are lined with cells with microvilli on

their apical surface. The circular folds, villi, and microvilli increase the surface area of the small intestine.



26.9a Gross Anatomy and Regions









The large intestine absorbs fluids and ions, and compacts undigestible wastes.











The large intestine is composed of the cecum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum, and

anal canal.



26.9b Histology









The large intestine mucosa lacks villi, but contains intestinal glands.











The outer longitudinal layer of the muscularis forms three discrete bands called teniae coli. The teniae coli cause the wall of the

colon to bunch into sacs called haustra.



26.9c Control of Large Intestine Activity





26.10 Accessory

Digestive Organs







Local autonomic reflexes regulate large intestine movements.



26.10a Liver









The liver receives venous blood from the hepatic portal vein and oxygenated blood from the hepatic artery proper.











Liver functions are bile production, drug detoxification, storage of nutrients and glycogen, and synthesis of plasma proteins.



26.10b Gallbladder









The gallbladder stores and concentrates bile produced by the liver.



26.10c Biliary Apparatus









The hepatic ducts drain bile into a single common hepatic duct, and the cystic duct merges with the common hepatic duct to form

the common bile duct.











The common bile duct and the pancreatic duct merge to empty their contents into the duodenum via the major duodenal papilla.



26.10d Pancreas









Pancreatic acini produce pancreatic juice that neutralizes acidic chyme.



26.11 Aging and the

Digestive System











Age-related changes in the digestive system lead to reduced secretions and diminished absorption of nutrients.



26.12 Development of

the Digestive System











The gut tube has a superior foregut, a central midgut, and an inferior hindgut.



26.12a Stomach, Duodenum, and Omenta Development









Stomach formation begins by week 4 of development. Differential growth rates cause the greater and lesser curvatures of the

stomach to form.



26.12b Liver, Gallbladder, and Pancreas Development









The liver parenchyma, gallbladder, and pancreas develop from endoderm outgrowths of the duodenum.



26.12c Intestine Development









The small and large intestines form from the midgut and hindgut beginning in week 5.



Chapter Twenty-Six  Digestive System







809



Challenge Yourself

Matching

Match each numbered item with the most closely related lettered

item.

1. circular folds



2. falciform ligament

3. pyloric sphincter



4.haustra

5.peristalsis

6. simple columnar



7.muscularis

8. stratified squamous

9. Peyer patches

10.submucosa













a.typically contains two layers of

smooth muscle

b.epithelium lining small intestine

c.contains dense irregular

connective tissue and blood

vessels

d.lymphatic nodules in wall of

ileum

e.attaches liver to anterior

abdominal wall

f.restricts chyme entry into small

intestine

g.epithelium lining the esophagus

h. sacs of large intestine wall

i.increase surface area of small

intestine

j.process to propel digested

materials through the

gastrointestinal tract



Multiple Choice

Select the best answer from the four choices provided.

1. Which organ is located in the right upper quadrant of the

abdomen?



a.liver



b.spleen



c. descending colon



d.appendix

2. The ______ cells of the stomach secrete hydrochloric acid

(HCl).



a.chief



b.parietal



c.mucous



d.enteroendocrine

3. Material leaving the ascending colon next enters the



a.cecum.



b. descending colon.



c. sigmoid colon.



d. transverse colon.

4. Which of these organs is retroperitoneal?



a.stomach



b. transverse colon



c. descending colon



d.ileum

5. Sympathetic innervation of the GI tract is responsible for



a. closing the pyloric sphincter.



b. stimulating peristalsis.



c. stimulating secretion of the pancreatic acinar cells.



d.vasodilating the major digestive system blood vessels.



6. The ______ is derived from the cranial part of the primary

intestinal loop.



a.jejunum



b.cecum



c. ascending colon



d.appendix

7. The main pancreatic duct merges with the ______, and their

contents empty into the duodenum through the major duodenal

papilla.



a. left hepatic duct



b. common bile duct



c. cystic duct



d. common hepatic duct

8. Which statement is false about pancreatic juice?



a.It is secreted through the main pancreatic duct into the

duodenum.



b. It is responsible for emulsifying (breaking down) fats.



c. It is produced by the acinar cells of the pancreas.



d. The juice has an alkaline pH.

9. The “living” part of a tooth is the



a.dentin.



b.cementum.



c.pulp.



d.enamel.

10. Most of the chemical digestion of our food occurs within the



a. large intestine.



b.pancreas.



c. small intestine.



d.esophagus.



Content Review

1. What initial stages of digestion occur in the oral cavity?

2. The GI tract from the esophagus to the anal canal is composed

of four tunics. Describe the general histology of the tunics and

the specific features of the stomach tunics.

3. Compare and contrast gastric juice and pancreatic juice with

respect to their composition and function.

4. Compare the anatomy and functions of the circular folds, villi,

and microvilli in the small intestine.

5. What are the teniae coli and haustra, and how are they

associated?

6. What is the function of each structure in the portal triad of the

hepatic lobule, and how do they work together to contribute to

the overall functioning of the liver?

7. What is the function of the gallbladder, and what role does it

play in digestion?

8. List in order the organs of the GI tract through which ingested

material travels, and describe the type(s) of digestion (mechanical/

chemical) that takes place in each organ. At what point is the

material called a bolus, chyme, and feces?

9. Why are there so many mucin-producing glands along the

length of the GI tract?

10. Describe how the small and large intestine form.



810



Chapter Twenty-Six  Digestive System



Developing Critical Reasoning

1. Alexandra experienced vomiting and diarrhea, and was

diagnosed with gastroenteritis (stomach flu). What specific

digestive system organs were affected by the illness, and how

did the illness interfere with each organ’s function?



2. Most cases of colorectal cancer occur in the most distal part of

the large intestine (the rectum, sigmoid colon, and descending

colon). Why do fewer instances of colon cancer tend to occur

in the proximal part of the large intestine? Include the anatomy

and function of the colon components in your explanation.



Answers to “What Do You Think?”

1. Saliva cleanses the mouth in a variety of ways. As saliva washes

over the tongue and teeth, it helps remove foreign materials

and buildup. Lysozyme in saliva is an antibacterial enzyme. A

person who has a dry mouth is not able to cleanse the mouth

well and is more likely to develop dental problems as a result of

built-up bacterial and foreign material.

2. A young child’s mouth is too small to support adult-sized teeth.

Deciduous teeth are much smaller and fit a child’s mouth better.

As the mouth increases in size by about age 6, it is able to

support the first adult-sized teeth.

3. The stomach is lined with specialized surface mucous cells that

secrete mucus onto the lining. This mucus prevents the acid

from eating away the stomach wall. In addition, the stomach

epithelial lining is constantly regenerating to replace any cells

that are damaged.



4. The duodenum has many circular folds so that the digested

materials can be slowed down and adequately mixed with

pancreatic juice and bile. The jejunum also has many circular

folds because the slowing down of the materials aids in

absorbing the maximum amount of nutrients. By the time chyme

reaches the distal ileum, most nutrient absorption has occurred,

and so the circular folds are not as essential.

5. When the gallbladder is removed, bile is still produced by the

liver, but it is secreted in a “slow drip.” A fatty meal requires

much more bile for digestion than the amount supplied by a

“slow drip,” causing the patient to experience gas, pain, bloating,

and diarrhea. Thus, surgical patients are initially told to limit

their fat intake. The body gradually adjusts so that more bile is

secreted, and thus a person may eventually be able to introduce

more fat back into his or her diet.



27



Outline

27.1  General Structure and Functions of the Urinary System

27.2 Kidneys

27.2a  Gross and Sectional Anatomy of the Kidney

27.2b  Blood Supply to the Kidney

27.2c  Innervation of the Kidney

27.2d Nephrons

27.2e  Collecting Tubules and Collecting Ducts: How Tubular Fluid

Becomes Urine

27.2f  Juxtaglomerular Apparatus



27.3  Urinary Tract

27.3a Ureters

27.3b  Urinary Bladder

27.3c Urethra



27.4  Aging and the Urinary System

27.5  Development of the Urinary System

27.5a  Kidney and Ureter Development

27.5b  Urinary Bladder and Urethra Development 



MODULE 13: URINARY SYSTEM



Urinary

System



812



Chapter Twenty-Seven  Urinary System



I



n the course of carrying out their specific functions, the cells

of all body systems produce waste products, and these waste

products end up in the blood. In this case, the blood is analogous

to a river that supplies drinking water to a nearby town. The river

water may become polluted with sediment, animal waste, and

motorboat fuel—but the town has a water treatment plant that

removes these waste products and makes the water safe to drink.

The urinary system is the body’s “water treatment plant.” Without

it, waste products could accumulate in the blood and kill us. This

chapter focuses on the organs of the urinary system and how they

work together to remove waste products from the blood and help

maintain homeostasis.



known as the urinary tract because they transport the urine out of

the body.

Besides removing waste products from the blood, the urinary

system performs many other functions, including the following:













27.1  General Structure and Functions



of the Urinary System



✓✓Learning Objectives







1. List and describe the primary organs of the urinary

system.

2. Explain the functions performed by the urinary system.

The organs of the urinary (yūr′i-nār′ē) system are the kidneys,

ureters, urinary bladder, and urethra (figure 27.1). The kidneys filter

waste products from the blood and convert the filtrate into urine

(yūr′in). The ureters, urinary bladder, and urethra are collectively







Storage of urine. Urine is produced continuously, but it would



be quite inconvenient if we were constantly excreting urine.

The urinary bladder is an expandable, muscular sac that can

store as much as 1 liter of urine.



Excretion of urine. The urethra transports urine from the

urinary bladder and expels it outside the body. In section 27.3b,

we discuss the expulsion of urine from the bladder, which is

called micturition or urination.



Regulation of blood volume. The kidneys control the

volume of interstitial fluid and blood under the direction of

certain hormones. Because changes in blood volume affect

blood pressure, the kidneys also indirectly affect blood

pressure.



Regulation of erythrocyte production. As the kidneys

filter the blood, they are also indirectly measuring the

oxygen level in the blood. If blood oxygen levels are

reduced, cells in the kidney secrete a hormone called

erythropoietin (ĕ-rith′rō-poy′ĕ-tin) (EPO; described in

sections 20.9a and 21.4). Erythropoietin acts on stem cells

in the bone marrow to increase erythrocyte production.

Having more erythrocytes allows the blood to transport

more oxygen.



Diaphragm

Adrenal gland

Kidneys

Hilum

Renal artery

Renal vein

Inferior vena cava

Descending abdominal aorta

Ureters

Parietal peritoneum (cut)



Urinary

bladder

Urethra



(a) Anterior view



Figure 27.1

Urinary System. The urinary system is composed of two kidneys, two ureters, a single urinary bladder, and a single urethra, shown here in (a) anterior and

(b) posterior views. (Components of the urinary system are labeled in bold font.)

(a, right) © McGraw-Hill Education/Christine Eckel



Chapter Twenty-Seven  Urinary System







Table 27.1



Urinary System Organs and Their Functions



Organ



Location



Description/Characteristics



Function



Kidneys



Diaphragm

Posterior abdominal wall;

right

kidney is inferior to left

kidneygland

Adrenal

Kidneys

Extend from kidneys to trigone

of bladder, along posteriorHilum

abdominopelvic wall Renal artery

Pelvic cavity, posterior to

pubicvein

Renal

symphysis (when full, it extends into

Inferiorcavity)

vena cava

inferior part of abdominal



Paired, bean-shaped organs; composed of outer cortex and

inner medulla



Filter blood and process filtrate into

tubular fluid, then urine



Paired thin, fibromuscular tubes composed of inner

mucosa, middle muscularis of smooth muscle, and an outer

adventitia



Transport urine from kidney to

urinary bladder via peristalsis



Ureters



Urinary bladder



Urethra











813







Muscular distensible sac composed of inner mucosa, a

submucosa, a muscularis, and an outer adventitia or serosa

The neck of the bladder is the inferior constricted region

where bladder and urethra meet; contains internal urethral

Descending abdominal aorta

sphincter



Inferior to neck of urinary bladder;

Single muscular tube; 3–5 cm long in females; 18–20 cm

Ureters

extends through muscles of pelvic

long in males

floor and opens into perineum

Parietal peritoneum (cut)



Regulation of ion levels. The kidneys help control the blood’s



Urinary ions (K+),

ion balance, such as sodium ions (Na+), potassium

bladder

2+

calcium ions (Ca ), and phosphate ions (PO43− ) by eliminating

varying amounts of these ions in the urine, depending upon

Urethra

dietary intake.



Regulation of acid-­base balance. The kidneys aid in

maintaining acid-base balance by altering blood levels of both

hydrogen ions (H+) and bicarbonate ions (HCO3− ) by also

eliminating varying amounts of these ions.



Reservoir for urine until micturition

(urination) occurs



Transports urine from urinary

bladder to outside of body



Table 27.1 summarizes the organs of the urinary system and

their functions.





W H AT D I D YO U LE A R N ?

1



2





What organs make up the urinary tract, and what is the main

function of the urinary tract?

Describe the mechanisms by which the kidneys regulate

blood volume and erythrocyte production.



(a) Anterior view



Adrenal

gland



T12 vertebra

12th rib



Left kidney

Right kidney



L3 vertebra



Ureters



Urinary

tract



Urinary

bladder

Urethra



(b) Posterior view



814



Chapter Twenty-Seven  Urinary System



27.2  Kidneys



✓✓Learning Objectives

3. Describe the anatomy of the kidneys.

4. Outline the fundamentals of filtration, tubular reabsorption,

and tubular secretion.

5. List the components of a nephron, and explain their roles in

urine formation.

The kidneys are two symmetrical, bean-shaped, reddish-brown

organs located along the posterior abdominal wall, lateral to the

vertebral column (figure 27.1). Each kidney weighs about 100 grams

and measures about 12 centimeters (cm) in length, 6.5 cm in width,

and 2.5 cm in thickness.

W H AT D O YO U TH I N K ?

1





A person must have at least one functioning kidney to

survive. Why do you think a lack of kidneys is deadly?



27.2a  Gross and Sectional Anatomy of the Kidney

The kidneys are retroperitoneal, because their anterior surface

is covered with parietal peritoneum and the posterior aspect lies

directly against the posterior abdominal wall. The superior pole



(also called superior extremity) of the left kidney is at about

the level of the T12 vertebra, and its inferior pole (also called

inferior extremity) is at about the level of the L 3 vertebra. The

superior pole of the right kidney is positioned about 2 cm inferior

to the superior pole of the left kidney to accommodate the large

size of the liver. An adrenal gland rests on the superior pole of

each kidney.

The kidney has a concave medial border called the hilum

(hī′lŭm; hilum = a small bit), where vessels, nerves, and the ureter enter and/or exit the kidney. The hilum is continuous with an

internal space within each kidney called the renal (rē′năl; ren =

kidney) sinus. The renal sinus houses renal arteries, renal veins,

lymph vessels, nerves, the renal pelvis, renal calyces, and a variable

amount of adipose connective tissue. The kidney’s lateral border

is convex.

Each kidney is surrounded and supported by several tissue layers. From innermost (closest to the kidney) to outermost, these layers

are the fibrous capsule, perinephric fat, renal fascia, and paranephric

fat (figure 27.2):









The fibrous capsule (kap′sūl; capsa = box) or renal capsule,



directly adheres to the outer surface of the kidney and is

composed of dense irregular connective tissue. The fibrous

capsule maintains the kidney’s shape, protects it from trauma,



Anterior



Stomach

Pancreas

Small intestine

Large

intestine



Descending

abdominal aorta

Inferior vena cava



Renal vein



Liver

Right kidney

Parietal peritoneum

Paranephric fat

Renal fascia



Body of

L2 vertebra



Renal artery

Renal hilum

Left kidney

Spleen



Perinephric fat

Fibrous capsule



Posterior



Figure 27.2

Position and Stabilization of the Kidneys. An inferior cross-sectional view (which is the view typically used in CT scans) shows that the kidneys are positioned

on the posterior abdominal wall and are covered on their anterior surface by the parietal peritoneum and surrounded by four concentric tissue layers (from

innermost to outermost); fibrous capsule, perinepheric fat, renal fascia, and paranephric fat.



815



Chapter Twenty-Seven  Urinary System





and helps prevent infectious pathogens from entering the

kidney.

■ The perinephric fat (peri = around, near; also called perirenal

fat, or adipose capsule) is external to the fibrous capsule and

contains adipose connective tissue that varies in thickness.

This layer, which is also called the perirenal fat, completely

surrounds the kidney and offers cushioning and support.

■The renal fascia (fash′ē-ă; a band) is external to the

perinephric fat and is composed of dense irregular connective

tissue. It anchors the kidney to the posterior abdominal wall

and peritoneum.

■The paranephric fat (para = next to; also called pararenal

fat, or paranephric body) is the outermost layer surrounding

the kidney. It is composed of adipose connective tissue and lies

between the renal fascia and the peritoneum.

When a kidney is sectioned along a coronal plane, an outer

renal cortex and an inner renal medulla can be seen (figure 27.3).

The medulla tends to be a darker shade than the cortex. Extensions

of the cortex, called renal columns, project into the medulla

and subdivide the medulla into renal pyramids (or medullary

pyramids). An adult kidney typically contains 8 to 15 renal

pyramids. The wide base of a renal pyramid lies at the external

edge of the medulla where the cortex and medulla meet, called the

corticomedullary junction (or corticomedullary border). The apex

(tip) of the renal pyramid (called the renal papilla) projects toward

the renal sinus.

Each renal papilla projects into a funnel-shaped space called

the minor calyx (kā′liks; pl., calyces, or calices, kal′i-sēz; cup of

a flower). There are between 8 and 15 minor ­calyces—in other

words, one minor calyx for each renal papilla. Several minor

calyces merge to form a larger space called a major calyx—each



kidney typically contains two or three major calyces. Urine from

the renal pyramids is collected by the minor calyces and then

drained into the major calyces. The major calyces merge to form

a large, funnel-shaped renal pelvis, which collects urine and

transports it into the ureter.

A human kidney is divided into 8 to 15 renal lobes. A renal

lobe consists of a medullary pyramid and some cortical substance

immediately surrounding the renal pyramid.





W H AT D I D YO U LE A R N ?

3



4





Where are the renal cortex and the renal medulla

located?

Why is the right kidney more inferiorly placed than the

left kidney?



27.2b  Blood Supply to the Kidney

Because the kidneys’ primary function is to filter the blood, at least

20–25% of the blood normally flows through the kidneys via the

pathway shown in figure 27.4. Blood is carried to a kidney in a renal

artery, which generally arises and extends from the lateral region

of the descending abdominal aorta at the level of the first or second

lumbar vertebra. Up to five segmental (seg-men′tăl) arteries branch

from the renal artery within the renal sinus. While still in the renal

sinus, the segmental arteries further branch to form the interlobar

(in′tĕr-lō′bar; inter = between, lobos = lobe) arteries. Interlobar arteries travel through the renal columns toward the corticomedullary

junction, where they branch to form arcuate (ar′kyū-āt; arcuatus =

bowed) arteries. These arcuate arteries project parallel to the base of

the medullary pyramid at the corticomedullary junction. The arcuate

arteries give off branches called interlobular (in′tĕr-lob′yū-lăr)



Renal cortex

Renal column



Renal medulla



Minor calyx



Renal pyramid



Renal sinus

contains:

Minor calyx

Major calyx



Renal column



Renal pelvis



Corticomedullary junction



Renal pelvis



Renal

papilla



Renal artery

Renal vein



Major calyx

Renal lobe

Ureter

Fibrous capsule



Ureter

Right kidney, coronal section



Figure 27.3

Kidney. A coronal section through the right kidney reveals the external cortex, the internal medulla, and urine drainage areas of the kidney.

(left) © McGraw-Hill Education/Rebecca Gray



Tài liệu bạn tìm kiếm đã sẵn sàng tải về

12b Liver, Gallbladder, and Pancreas Development

Tải bản đầy đủ ngay(0 tr)

×