Genito-Urinary System

What are the functions of the kidneys?

- Acid balance
- Water balance
- Electrolyte balance
- Toxin removal
- Blood pressure control
- Erythropoietin production
- Vitamin D metabolism

What are electrolytes?

Salts with an electrical charge vital for heart and nervous system

What are the waste products in the body?

- Ammonia: from breakdown of amino acids in liver
- Uric acid: from cell breakdown in liver
- Urea: from ammonia

What are the functions of the different parts of the kidney?

- Cortex filters blood to form urine
- Medulla collects and excretes urine
- Urine drains into calyces to the renal pelvis and out through the ureter

What are the 2 distinct regions of the kidney?

- Renal cortex
- Renal medulla

What is the structure of the renal cortex?

Forms a shell around the medulla and dips into the medulla between renal pyramids forming renal columns

What is the structure of the renal medulla?

Composed of conical masses of tissue called renal pyramids that appear striated

What is the appearance of the renal medulla and renal cortex?

The granular appearance of the cortex and the striations of the medulla are due to the organisation of the tiny renal corpuscles and renal tubules associated with the nephron

What forms the renal pelvis?

The superior end of the ureter forms a funnel-shaped sac called the renal pelvis inside the sinus

How is the renal pelvis divided?

Into 2 or 3 tubes called major calyces which are divided into several minor calyces in which renal papillae form

What is a nephron?

The functional unit of the kidney

How many nephrons are located in each kidney?

Approximately 1-2million

What is the nephron formed of?

Made of blood vessels and tubules which collect filtrate to become urine

What are the 5 areas of the nephron?

- Glomerulus and Bowman's Capsule
- Proximal Convoluted Tubule
- Loop or Henle
- Distal Convoluted Tubule
- Collecting Duct

What is the function of the Glomerulus and Bowman's Capsule?

- Site of filtration with clusters of capillaries
- Capsule is a cup shaped structure with cuboidal epithelial cells with a basement membrane separating the blood side from the renal tubule

What is the function of the Proximal Convoluted Tubule?

Selective reabsorption of filtrate

What is the function of the Loop of Henle?

Cells change and allow selective reabsorption of water and sodium to concentrate or dilute urine

What is the function of the Distal Convoluted Tubule?

Site of fine tuning, reabsorption and secretion

What is the function of the Collecting Duct?

Concentration and carrying of urine to renal pelvis

What is the functions of the nephron?

- Glomerular Filtration
- Reabsorption
- Secretion

What is glomerular filtration?

Water, electrolytes and waste pushed out of blood

What is reabsorption in the nephron?

Process of returning important substances from the filtrate back to the body

What is secretion in the nephron?

Movement of materials from the body into the filtrate

What is the structure of the arteries in the kidney?

- Enters the kidney through the hilum and gives off several branches, called interlobar arteries which pass between the renal pyramids
- The interlobular arteries branch, forming a series of incomplete arches, the arcuate arteries, which in turn give rise to cortical radiate arteries
- The final branches of the cortical radiate arteries are called afferent arterioles

What is the pathway of blood supply to the kidneys?

- Venous return corresponds with arterial pathways and blood leaves the kidney in the renal vein before joining the inferior vena cava
- The cluster of capillaries that forms a glomerulus arise from an afferent arteriole
- After passing through the glomerular capillaries, blood enters an efferent arteriole
- The efferent arteriole typically branches into a complex, interconnecting network of capillaries, called the peritubular capillary system that is closely associated with the renal tubule
- After flowing through the peritubular capillary network, the blood enters the venous system of the kidney

What is glomerular filtration?

- Urine formation begins when water and certain dissolved substances are filtered out of glomerular capillaries and into glomerular capsules to create filtrate
- Many fenestrae make capillary walls permeable

What is filtered in and out of the filtrate?

- In filtrate is small molecules e.g. water, glucose, electrolytes
- Filtered out of the filtrate is large proteins and red blood cells

What is the glomerular filtration rate?

- Healthy person 125ml/min
- 180l per day filtered
- 1-2l of urine produced

What is proportional to net filtration rate?

eGFR

What factors affect GFR?

- Change in plasma osmotic pressure
- Change in diameter of afferent and efferent arterioles

What happens to GFR when different arterioles are constricted and relaxed?

- Afferent arterioles constrict = GFR falls
- Efferent arterioles constrict = GFR rises
- Afferent arterioles relax = GFR rises
- Efferent arterioles relax = GFR falls

Why might GFR increase or decrease?

When bodily fluids are in excess or when they are sparse and the body is conserving fluid

What do the sympathetic nervous system reflexes respond to?

Changes in blood pressure and volume to stimulate release of renin and vasoconstriction of arterioles

What do juxtaglomerular cells secrete renin in response to?

- Decreased blood pressure
- Sympathetic stimulation
- Macula densa

What do Macula densa cells do?

- Sense decrease in chloride, potassium and sodium ions in ascending loop of Henle

What is the RAAS system?

- Kidneys sense a decrease in blood pressure and release renin from the juxtaglomerular cells
- Renin converts angiotensinogen to angiotensin 1
- In the lungs, angiotensin converting enzyme converts angiotensin 1 to angiotensin 2
- Angiotensin 2 causes vasoconstriction, resulting in increased blood pressure
- Angiotensin 2 also stimulates the adrenal glands to release aldosterone
- Within the kidneys, aldosterone promotes reabsorption of sodium and water
- The circulating blood volume increases, raising the blood pressure

How is the kidney extrinsically regulated?

- Atrial natriuretic peptide (ANP) is released in response to an increase in blood pressure or volume
- Increases GFR which inhibits renin and dilates afferent arterioles

How does reabsorption occur in the kidney?

- Where important substances from the filtrate are reabsorbed back into the body
- Glucose, electrolytes, vitamins, amino acids and water are reabsorbed by osmosis and active transport
- Reabsorption occurs in the proximal convoluted tubule and descending loop of Henle

What occurs in each limb of the loop of Henle?

- Descending: reabsorption of water as cells are highly permeable
- Ascending: reabsorption of sodium, potassium and chloride ions by active transport

How does secretion occur in the kidneys?

- Glomerulus doesn't filter all the blood
- Any waste products left in the blood are secreted back into tubules via active transport and diffusion

What is reabsorbed in the distal convoluted tubule?

- Sodium by active transport
- Water by osmosis

What is secreted in the distal convoluted tubule?

- Hydrogen, ammonia and potassium ions by active and passive electrochemical attraction
- Sodium and potassium pump

What is the homeostatic mechanism for if the blood is too concentrated?

- ADH is released from pituitary gland
- ADH stimulates tubular reabsorption in the kidney so that more fluid is reabsorbed into the body
- Once blood concentration has returned to normal, ADH will stop being released
- Thirst centre in brain is also switched on to make you drink more

What is the homeostatic mechanism for if there is too much water in the blood?

- Pituitary gland releases less ADH
- Less water is reabsorbed by the kidneys
- More water leaves as urine

What affects does alcohol have on the body?

- Diuretic
- Inhibits the production of ADH
- Reduces water reabsorption
- Leads to dehydration

What are the layers of the bladder?

- Mucous coat
- Sub mucous coat
- Detrusor muscle
- Serous coat

What is the micturition reflex?

- Bladder holds 400-600mls
- Urge to urinate at 150mls
- Sensation of fullness at 300mls

How does urination occur?

- External sphincter relaxes
- Detrusor muscle contracts
- Urine excreted in urethra
- Stretch receptors aren't stimulated, detrusor relaxes and bladder fills again

What is normal urine?

- 1-2l/day
- Pale yellow
- Transparent when fresh
- Mildly aromatic
- Diabetic urine may smell fruity due to ketones
- pH of 4.6-8