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Urinary System - Human Anatomy - Lecture Notes, Study notes of Anatomy

Alagappa UniversityAnatomy

Urinary System, Regulation of Blood Volume, Contribution to Metabolism, Urinary Bladder, Histology of Kidneys, Adipose Capsule, Outer Renal Fascia, Parenchyma, Kidney Functional Tissue are some points f this lecture. This lecture handout was provided by lecturer in Human Anatomy class. Important terms are bold in this handout. Few terms of the lecture are given above.

Typology: Study notes

2011/2012

Uploaded on 12/24/2012

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A. Introduction
1. The major function of the urinary system is to help maintain homeostasis by controlling the
composition, volume, and pressure of blood, and removing wastes from the blood; it does
so by removing and restoring selected amounts of water and solutes.
2. The urinary system consists of:
i. two kidneys which perform the above functions and consequently produce urine
ii. two ureters which drain urine from the kidneys and transport it to...
iii. one urinary bladder which stores urine until it is ready to be expelled
iv. one urethra which transports urine from the urinary bladder to the exterior; in
males, the urethra also transports semen
3. The kidneys perform several specific functions:
i. regulation of blood volume and composition
ii. regulation of blood pressure by secreting renin
iii. contribution to metabolism by:
a. performing gluconeogenesis
b. secreting erythropoietin
c. participating in synthesis of the active form of vitamin D
4. Nephrology is the medical specialty that deals with the anatomy, physiology, and
pathology of the kidney; urology is the branch of medicine that deals with the male and
female urinary systems and the male reproductive system.
B. Anatomy and Histology of the Kidneys
1. The paired reddish kidneys are retroperitoneal organs attached to the posterior
abdominal wall just above waist level
i. they are positioned between the levels of the last thoracic and the third lumbar
vertebrae
ii. they are partially protected by the eleventh and twelfth pairs of ribs
iii. the right kidney is slightly lower than the left because of the presence of the liver
on the right side
2. External Anatomy:
i. near the center of the kidney’s concave medial border is a depression called the
renal hilus through which travel:
a. ureter
b. blood vessels and lymphatic vessels
c. nerves
- the hilus is the entrance to a cavity in the kidney called the renal sinus
ii. the kidney is surrounded by three layers of tissue:
a. inner renal capsule
b. intermediate adipose capsule
c. outer renal fascia
3. Internal Anatomy:
i. the kidney’s functional tissue, called the parenchyma, has:
a. outer layer called the renal cortex
b. inner region called the renal medulla
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A. Introduction

  1. The major function of the urinary system is to help maintain homeostasis by controlling the composition, volume, and pressure of blood, and removing wastes from the blood; it does so by removing and restoring selected amounts of water and solutes.
  2. The urinary system consists of: i. two kidneys which perform the above functions and consequently produce urine ii. two ureters which drain urine from the kidneys and transport it to... iii. one urinary bladder which stores urine until it is ready to be expelled iv. one urethra which transports urine from the urinary bladder to the exterior; in males, the urethra also transports semen
  3. The kidneys perform several specific functions: i. regulation of blood volume and composition ii. regulation of blood pressure by secreting renin

iii. contribution to metabolism by: a. performing gluconeogenesis b. secreting erythropoietin c. participating in synthesis of the active form of vitamin D

  1. Nephrology is the medical specialty that deals with the anatomy, physiology, and pathology of the kidney; urology is the branch of medicine that deals with the male and female urinary systems and the male reproductive system.

B. Anatomy and Histology of the Kidneys

  1. The paired reddish kidneys are retroperitoneal organs attached to the posterior abdominal wall just above waist level i. they are positioned between the levels of the last thoracic and the third lumbar vertebrae ii. they are partially protected by the eleventh and twelfth pairs of ribs iii. the right kidney is slightly lower than the left because of the presence of the liver on the right side
  2. External Anatomy : i. near the center of the kidney’s concave medial border is a depression called the renal hilus through which travel: a. ureter b. blood vessels and lymphatic vessels c. nerves
  • the hilus is the entrance to a cavity in the kidney called the renal sinus ii. the kidney is surrounded by three layers of tissue: a. inner renal capsule b. intermediate adipose capsule c. outer renal fascia
  1. Internal Anatomy : i. the kidney’s functional tissue, called the parenchyma, has: a. outer layer called the renal cortex b. inner region called the renal medulla

ii. the medulla contains 8-18 cone-shaped renal pyramids whose apexes are called renal papillae iii. the renal cortex is divided into: a. outer cortical zone b. inner juxtamedullary zone

  • renal columns are portions of the cortex that extend between renal pyramids; a renal lobe consists of a renal pyramid, its overlying area of renal cortex, and half of each adjacent renal column iv. within the parenchyma are the functional units of the kidney called nephrons which produce urine; urine from the nephrons drains into papillary ducts and onwards into minor calyces which merge to form major calyces that deliver the urine into a large cavity called the renal pelvis (the renal pelvis is located within the renal sinus ); urine then exits the kidney by flowing into a ureter
  1. Blood and Nerve Supply :

i. blood flows through kidneys via the following sequence of blood vessels:

a. right and left renal arteries b. segmental arteries c. interlobar arteries d. arcuate arteries e. interlobular arteries f. afferent arterioles g. glomeruli (singular is glomerulus ) h. efferent arterioles i. peritubular capillaries which enmesh the proximal and distal convoluted tubules

  • efferent arterioles of juxtamedullary nephrons also give rise to vasa recta which dip down alongside the loop of Henle into the medulla j. peritubular venules k. interlobular veins l. arcuate veins m. interlobar veins n. right and left renal veins (each exits at the renal hilus) ii. the nerve supply to the kidneys is primarily vasomotor and derives from the celiac ganglion and renal plexus of the sympathetic division of the ANS
  1. Nephron : i. each kidney’s parenchyma contains about one million nephrons; the nephron is the functional unit of the kidney which filters blood, returns useful substances to blood, and removes unwanted substances from the blood, thereby producing urine ii. the nephron consists of two portions: a. renal corpuscle , where plasma is filtered b. renal tubule , into which the filtered fluid passes iii. the renal corpuscle has two components: a. network of capillaries called the glomerulus
  • receives blood from an afferent arteriole
  • blood drains into an efferent arteriole b. surrounding the glomerulus is a double-walled epithelial cup called the glomerular (Bowman’s) capsule iv. as blood flows through the glomerulus, a filtrate of the blood plasma enters the capsular space v. the filtered fluid then flows into the renal tubule, which consists of three segments:

C. Functions of Nephrons

  1. Urine formation involves three major processes: i. glomerular filtration a. blood flowing through a glomerulus is filtered by the filtration membrane or endothelial-capsular membrane resulting in formation of a glomerular filtrate which contains all blood components except: 1. formed elements 2. most plasma proteins b. the filtration membrane consists of:
  2. glomerular endothelial cells with fenestrations and mesangial cells
  3. basal lamina
  4. podocytes with pedicels and filtration slits and associated slit membrane ii. tubular reabsorption a. as the filtrate flows through a renal tubule about 99% of it is reabsorbed into blood in the peritubular capillaries or vasa recta b. the substances reabsorbed include glucose, amino acids, urea, various ions, and most of the water along with most small proteins and peptides that passed through the filter c. therefore, tubular reabsorption returns needed substances to the blood iii. tubular secretion a. substances are transported from the blood in peritubular capillaries into the filtrate flowing through the renal tubule b. the substances secreted include hydrogen ions, other excess ions, creatine and other wastes, and certain drugs c. therefore, tubular secretion helps control blood pH and helps eliminate unwanted substances from the body

D. Ureters

  1. From the renal pelvis, urine drains into a ureter which exits the kidney at the renal hilus.
  2. The ureters are retroperitoneal and enter the urinary bladder medially from the posterior aspect.
  3. There is no anatomical valve but there is a functional valve at the opening of each ureter into the urinary bladder: Each ureter passes obliquely through the wall of the urinary bladder to create an effective physiological valve which prevents backflow of urine since filling of the urinary bladder with urine compresses the oblique openings into the ureters.
  4. The wall of each ureter consists of three layers: i. inner mucosa with transitional epithelium lying over lamina propria ii. intermediate muscularis consists of: a. inner longitudinal layer of smooth muscle tissue b. outer circular layer of smooth muscle tissue c. extra outer longitudinal layer in the distal third of the ureter - the muscularis is responsible for peristalsis iii. outer adventitia which has extensions that anchor the ureters in place.
  5. The function of the ureters is to transport urine into the urinary bladder; transport is accomplished by: i. peristaltic waves ii. hydrostatic pressure iii. gravity
  6. The ureters receive blood from the renal, testicular or ovarian, common iliac, and inferior vesical arteries; blood drains into the corresponding veins.
  1. The ureters are innervated by the renal plexuses, which are supplied by sympathetic and parasympathetic fibers from the lesser and lowest splanchnic nerves.

E. Urinary Bladder

  1. The urinary bladder is a hollow muscular organ located retroperitoneally in the pelvic cavity posterior to the pubic symphysis i. in males, it is directly anterior to the rectum ii. in females, it is anterior to the vagina and inferior to the uterus and it usually has a smaller capacity
  2. The shape of the urinary bladder ranges from collapsed to spherical to pear-shaped, depending on the volume of urine it contains.
  3. The floor of the urinary bladder has a small triangular area called the trigone i. the two posterior corners contain the two ureteral openings ii. the anterior corner contains the internal urethral orifice iii. because its mucosa is firmly bound to the muscularis, the trigone has a smooth appearance
  4. The wall of the urinary bladder consists of three layers: i. inner mucosa with transitional epithelium lying over lamina propria a. except in the trigone, rugae are also present b. these features permit the urinary bladder to continually inflate and deflate ii. intermediate detrusor muscle (the muscularis )which consists of three layers of smooth muscle tissue: a. inner longitudinal layer b. middle circular layer c. outer longitudinal layer - around the opening to the urethra, the circular fibers form an internal urethral sphincter - below the internal sphincter is the external urethral sphincter, which is composed of skeletal muscle and is a modification of the urogenital diaphragm muscle iii. outer adventitia with serosa on the superior surface of the bladder
  5. Urine is expelled by micturition (urination or voiding) i. accumulation of urine in the urinary bladder stimulates stretch receptors which initiate nerve impulses delivered to the spinal cord’s micturition center which in turn initiates a parasympathetic spinal micturition reflex ; the latter involves contraction of the detrusor muscle and relaxation of the internal urethral sphincter accompanied by relaxation of the external urethral sphincter ii. the cerebral cortex may voluntarily initiate or delay micturition for a limited period of time
  6. The urinary bladder receives blood from the superior, middle, and inferior vesical arteries; blood drains into the internal iliac veins.
  7. The nerves of the urinary bladder are derived partly from the hypogastric sympathetic plexus and partly from the second and third sacral nerves.

F. Urethra

  1. The urethra is a tube leading from the floor of the urinary bladder to the exterior i. in females: a. it lies directly posterior to the pubic symphysis and is embedded in the anterior wall of the vagina b. it is about 6 mm wide and 4 cm long c. it leads to the external urethral orifice which is located between the clitoris and vaginal opening ii. in males:

H. Aging and the Urinary System

  1. With aging, the kidneys decrease in size and become less effective at cleansing blood.
  2. Urinary system disorders associated with aging include: i. acute and chronic kidney inflammation ii. renal calculi iii. susceptibility to dehydration iv. urinary tract infections v. polyuria vi. nocturia vii. increased frequency of urination viii. dysuria ix. urinary retention x. incontinence xi. hematuria

I. Key Medical Terms Associated with the Urinary System

  1. Students should familiarize themselves with the glossary of key medical terms.