Kidney Function and Anatomy Quiz

Urinary System Overview

• The Urinary System is responsible for water control and nitrogen disposal.
• It comprises several key organs: kidneys, ureters, urinary bladder, and urethra.

Organs of the Urinary System

• Kidneys: Bean-shaped organs located in the dorsal body wall, between T12 and L3 vertebrae. The right kidney is positioned slightly lower than the left. Attached to ureters, renal blood vessels, and nerves at the renal hilus. Each kidney has an adrenal gland.
• Ureters: Slender tubes connecting the kidneys to the bladder. They run behind the peritoneum. Peristalsis aids in urine transport.
• Urinary Bladder: A smooth, collapsible muscular sac that temporarily stores urine. It extends significantly without causing increased internal pressure.
• Urethra: A thin-walled tube carrying urine from the bladder to the exterior. Urine release is controlled by internal and external sphincters.
• Note gender-specific urethra differences: length and location

Kidney Structures

• Each kidney has a concave medial border, hilum, and convex lateral border.
• Blood and lymph vessels and nerves enter and exit through the hilum.
• Medullary pyramids - triangular regions of tissue in the medulla.
• Renal columns - extensions of cortex-like material inward.
• Calyces: cup-shaped structures funneling urine toward the renal pelvis.

Regions of the Kidney

• Renal cortex: The outer region of the kidney.
• Renal medulla: Located inside the cortex.
• Renal pelvis: The inner collecting tube of the kidney.

Kidney Division

• The kidney is divided into an outer cortex and inner medulla.
• The medulla consists of conical or pyramidal structures called medullary pyramids.
• Medullary rays arise from the base of each medullary pyramid and are parallel arrays of tubules.

Kidney Size

• An adult kidney measures approximately 12 cm (5 inches) in length, 6 cm (2.5 inches) in width, and 3 cm (1 inch) in thickness.

Anatomy of the Kidney

• The main structures of the mammalian kidney include: kidney cortex, renal medulla, renal pelvis, and nephrons.

Blood Flow in the Kidneys

• Blood flows from the aorta through renal, segmental, lobar, interlobar, arcuate, and interlobular arteries.
• Blood then flows through the glomerulus (capillaries) into peritubular capillaries.
• The blood exits through interlobular and other veins.

Anatomy of the Nephron

• Glomerulus: A tuft of capillaries surrounded by Bowman's capsule. Filtration occurs here.
• Proximal tubule: Receives the filtered fluid from Bowman's capsule.
• Loop of Henle: Establishes a concentration gradient for water reabsorption.
• Distal tubule: Reabsorbs essential substances and secretes wastes.
• Collecting duct: Collects the filtrate from several nephrons before it becomes urine.

Nephron

• An individual kidney contains around 4 million nephrons; each nephron is the kidney's fundamental unit.
• Each nephron comprises a renal corpuscle and a renal tubule.
• The renal corpuscle is a double-walled epithelial capsule, Bowman's capsule, enclosing the glomerulus (a tuft of capillaries).

Renal Corpuscles

• Each renal corpuscle is about 200 µm in diameter.
• It comprises a tuft of capillaries, glomerulus.
• The glomerulus is encompassed by a double-walled epithelial capsule, Bowman's capsule, which has an internal layer (visceral) and an external layer (parietal).
• The urinary space is present between the parietal and visceral layers.
• Afferent arterioles enter, and efferent arterioles leave through the vascular pole.
• The proximal convoluted tubule starts at the urinary pole.

Glomerulus, filtration of blood

• The glomerulus acts as the sole filtration site.
• Blood pressure pushes plasma through capillary walls into Bowman's capsule.

Proximal Tubule, reabsorption of materials

• Nutrients (salts, vitamins) are moved out of the proximal tubule through active transport.
• Water follows the nutrients by osmosis.

Loop of Henle

• Interstitial fluid surrounding the loop of Henle is elevated in sodium chloride concentration.
• This enables water to passively diffuse out of the loop.

Distal Tubule, secretion of wastes, control of ions

• Active transport is instrumental in releasing more nutrients and regulating the level of concentrated urine.
• Ions, drugs, and toxins are also actively secreted into the tubule.

Collecting Duct

• Water is passively released from the tube through osmosis, as the tube is surrounded by saline tissue.
• Urea is removed through diffusion.

Juxtaglomerular Apparatus (JGA)

• A specialized structure near the glomerulus.
• A crucial component of the nephron and plays a vital role in regulating blood pressure, blood volume, and filtration rate.

Blood Pressure Regulation (RAAS)

• Renin is released by the JGA in response to low BP.
• Renin converts angiotensinogen (liver protein) to angiotensin I.
• Angiotensin-converting enzyme (ACE) converts angiotensin I into angiotensin II.
• Angiotensin II causes vasoconstriction and stimulates aldosterone release.
• Aldosterone retains water and sodium, increasing blood volume and pressure.

Functions of the Kidney

• Filtration: Kidneys filter gallons of fluid from the bloodstream per day.
• Waste processing: The kidneys process the filtrate, removing wastes and excess ions to leave the body in urine while returning needed substances to the blood (e.g. salts, etc).
• Elimination: Kidneys are mainly responsible for eliminating nitrogenous wastes, toxins, and drugs from the body, however other organs play a role as well

Kidney Hormones

• Renin: Regulates blood pressure.
• Erythropoietin: Stimulates red blood cell production in the bone marrow.
• Vitamin D: Kidney cells convert vitamin D to its active form.

Urea Removal

• Kidneys remove urea from the bloodstream, urea being a result of proteins broken down in the body.

Amino Acid Metabolism and Ammonia

• The liver converts ammonia into urea.
• Ammonia is toxic, while urea is less toxic.

Regulating Water (ADH)

• Antidiuretic hormone (ADH) regulates water balance.
• ADH increases the permeability of the distal tubule, which causes an increase in water recovery.

Caffeine and Alcohol

• Caffeine and alcohol are diuretics, they cause increased water loss.
• Alcohol inhibits ADH release.
• Caffeine interferes with ADH activity.

Water balance

• Water intake must equal water output.
• Water is necessary for numerous body functions.

Water and Electrolytes

• Changes in electrolyte balance lead to water movement between compartments.

Variations in Urine Production

• Dilute urine results from excessive water intake.
• Concentrated urine arises from significant water loss.

Kidney Development

• Functional kidneys typically develop during the third month of gestation.
• Newborns' bladders are smaller and cannot concentrate urine efficiently.

Aging and the Urinary System

• Aging involves decline in urinary function, bladder shrinkage, and increased urinary retention in males.

Urethra: Gender Differences

• Females have a short urethra, while males have a long one.
• Functionally, both genders' urethras only carry urine.

Voiding (Micturition)

• Voiding involves the simultaneous opening of both sphincters, (external and internal)
• The internal sphincter relaxes.
• Pelvic splanchnic nerves trigger the external sphincter relaxation.

Water Balance: Different Ages

• Young adults have different water composition percentages in their body compared to babies or old age individuals.