Renal Anatomy
Major Organs:
[Section 25.2: Gross Anatomy of Urine Transport]
· kidneys
· ureters
· urinary bladder
· urethra
Functions:
[Section: Introduction (chapter 25)]
· filters dissolved material from the blood
· regulates electrolytes
· regulates fluid volume
· concentrates and stores waste products
· reabsorbs metabolically important substances back into the circulatory system
Urethra
[Figure 25.3: Female and Male Urethras]
· carries urine from the internal urethral orifice to the external urethral orifice and exits the body
· Note the basic differences in length between male and female ureters. What additional risk does this cause for females?
· Notice that the male urethra is a common exit for both the urinary and reproductive systems.
Urinary Bladder
· trigone – triangular region on the posterior wall of the urinary bladder – contains the ureteral openings, the entrance of the ureters to the urinary bladder – inferiorly the urethra exits
· inner surface lined with transitional epithelium (allows for expansion)
· detrusor muscles – in the wall of the bladder (expels urine from bladder)
· rugae – folds formed from epithelial lining
Ureters
· narrow, long, muscular tubes
· urine is moved by peristalsis from the kidney to the urinary bladder
Kidneys:
[Section 25.3: Gross Anatomy of the Kidney (all subsections)]
· located posterior to the parietal peritoneum
· basic anatomy:
o renal capsule
o renal cortex
o renal medulla
§ renal pyramid
§ renal column
§ renal papilla
o calyces (major and minor)
o renal pelvis
o renal hilum
Blood Flow through the Kidney
[Figure 25.9: Blood Flow in the Kidney]
Since the primary function of the kidneys is to filter waste materials from the blood, it is important for you to understand the complexities of the flow of blood into and out of the kidneys.
· Blood is delivered via the renal artery, which branches from the abdominal aorta
· Then it branches into segmental arteries then into interlobar arteries, which pass through renal columns
· Interlobar a. then divide into arcuate arteries, which cross the base of pyramids and enter the renal cortex as interlobular arteries
· These branch into afferent arterioles which are what forms the glomerulus
· At the end of the glomerulus, opposite the afferent arteriole, an efferent arteriole exits the glomerulus
· The efferent arteriole forms a bed of peritubular capillaries around the entire tubular portion of cortical nephrons
· But only around the proximal and distal convoluted tubules in juxtamedullary nephrons
· In juxtamedullary, the loop of henle is surrounded by vasa recta capillaries
· Both networks drain into interlobular veins, which drain into arcuate veins, to interlobar veins and finally the renal vein
Specific Kidney Functions
1. Remove waste: The kidneys filter waste products and excess fluid out of the blood and remove them from the body in the form of urine. (nitrogenous wastes such as urea and ammonium)
2. Maintain the right balance of chemicals in the body: The kidneys keep the right balance of chemicals, such as sodium, potassium, calcium, magnesium, and other substances your body needs to function properly. They filter excess amounts of these chemicals from the blood and get rid of them in the urine.
3. Synthesize several regulatory chemicals: The kidneys produce and secrete three important chemicals: renin, erythropoietin, and the active form of vitamin D (Calcitriol).
Production of Urine: An Overview
· The kidneys maintain the chemical balance of body fluids by removing metabolic wastes, excess water and electrolytes
· Three physiological process occur in nephrons to produce urine:
1. Filtration
o Blood is initially filtered in the glomerulus
2. Reabsorption
o as the filtrate moves through the PCT, 60-70% of water and 100% of the organic nutrients (glucose, amino acids) are reabsorbed into the blood
o The loop of Henle conserves water and salt while concentrating the filtrate for modification by the DCT
o Reabsorption in the DCT is controlled by two hormones, aldosterone and anitdiuretic hormone (ADH)
3. Secretion
o Most secretion takes place in the DCT
The Nephron
[Section 25.4: Microscopic Anatomy of the Kidney]
[Figure 25.10: Blood Flow in the Nephron]
· The basic functional unit of the kidney is the nephron
· Here, water, ions and other waste material are removed from the blood to produce filtrate
· The filtrate then circulates through tubules and anything still needed is absorbed back into the blood
· The remaining filtrate is excreted as urine
· 2 types of nephrons:
o Cortical make up about 85% of all nephrons in a kidney
o Juxtamedullary make up the other 15%
Nephron Anatomy
Each nephron consists of 2 distinct regions:
1. renal corpuscle – filters blood
2. renal tubule – modifies the filtrate through reabsorption and secretion to form urine
Nephron Part 1: The Renal Corpuscle
[Section 25.4.1.1: Renal Corpuscle]
[Figure 25.12: Fenestrated Capillary]
· initial filtration of blood
· Consists of two components: the glomerulus and Bowman’s capsule
· Filterable blood components such as water, nitrogenous waste, and nutrients form the glomerular filtrate.
· Non-filterable blood components such as blood cells and platelets remain in the blood and exit the glomerulus via the efferent arteriole.
Nephron Part 2: The Renal Tubule
· modifies the filtrate through reabsorption and secretion to form urine
· consists of multiple sections:
o the proximal convoluted tubule
o the nephron loop or loop of Henle; consists of two distinct parts:
§ descending limb
§ ascending limb
o the distal convoluted tubule
· all tubules empty into collecting ducts which channel urine towards the center of each kidney
Proximal Convoluted Tubule
[Section 25.4.1.2: Proximal Convoluted Tubule]
· the major site for reabsorption of water and solutes from the filtrate into the interstitial fluid and then into blood capillaries
· reabsorb 100% of most organic solutes (amino acid, glucose, etc.); 65% of water, sodium ions, and potassium ions; and 50% of chloride ions
Descending Limb (of nephron loop)
[Section 25.4.1.3: Loop of Henle]
· the nephron loop is also called the loop of Henle
· 15% of the water in the filtrate is reabsorbed by osmosis into the interstitial fluid
· the descending limb is impermeable to solutes
Ascending Limb (of nephron loop)
[Section 25.4.1.3: Loop of Henle]
· reabsorbs solutes
· impermeable to water
Distal Convoluted Tubule
[Section 25.4.1.4: Distal Convoluted Tubule]
· reabsorbs a small amount of water and solutes
· mainly, secretes solutes from the blood into the filtrate
· drains into a collecting duct
Collecting Ducts
[Section 25.4.1.5: Collecting Ducts]
· reabsorbs a small amount of water and solutes
· mainly, secretes solutes from the blood into the filtrate
· merge to form larger papillary ducts