Renal System Flashcards by Abi Wareham

Functions

Excretion of waste and toxins
Regulation of blood ionic composition
Maintenance of blood osmolarity
Regulation of blood pH
Regulation of blood pressure
Hormone production
Regulate blood glucose

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Kidneys

Either side of the vertebral column
Level T12-L3
Lateral - convex
Medial - concave
Renal cortex and renal medulla

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Nephrons

Functional units of the urinary system
Intricate system of tubules surrounded by blood vessels
Millions per kidney

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Glomerulus

Compact network of capillaries
Afferent and efferent arterioles

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Proximal convoluted tubule (PCT)

In renal cortex

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Loop of Henle

Begins in the cortex
Extends into the medulla
Ascending and descending limb

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Distal convoluted tubule (DCT)

Links loop of Henle with the collecting duct
In the cortex

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Collecting duct (CD)

Function to drain the renal tubules

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Glomerulus: Juxtaglomerular appparatus

Differentiated cells that occupy a region of the renal corpuscle
Role in the regulation of blood pressure, volume and osmolarity, secretion of renin

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Glomerulus: visceral layer

Fenestrations - small pores, blood plasma can go through
3.4-4.2 nm wide
No big molecules can not enter the filtrate

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Glomerulus: filtration membrane

Negative charge molecules can not enter the filtrate

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Glomerulus: podocytes

Stellate squamous epithelial cells
Projections that wrap around the capillaries

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Filtration

Blood is filtered - water and solutes move out
Glomerular filtrate
Renal corpuscle
Filtrate - glucose, amino acids, wastes, vitamins, electrolytes, nutrients, water.

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Glomerular filtrate rate

Rate the kidney/nephron filters the blood
GFR = 125ml/minute
180 tires of filtrate are produced per day

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Promotion of filtrate: net filtration pressure

Sum of all forces/pressure
From the glomerular capillaries to the capsular space

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Promotion of filtrate: glomerular blood hydrostatic pressure

55mmHg
In glomerular capillaries
Force liquid through the filtration membrane
Promotes filtration

Promotion of filtrate: blood colloid osmotic pressure

30mmHg
Presence of large proteins that cannot pass through the filtration membrane
Opposes filtration

Promotion of filtrate: capsular hydrostatic pressure

15mmHg
Presence of fluid already inside the capsular space and renal tubule
Prevents the passage of liquid through the filtration membrane
Opposes filtration

Auto-regulation

High pressure - afferent arterioles constrict
Low pressure - efferent arterioles constrict, afferent arterioles release renin

Tubular reabsorption

Water and solutes reabsorbed
Proximal convoluted tubule
Sodium is actively reabsorbed
Water, some ions and nutrients by osmosis, diffusion or facilitated diffusion

Tubular reabsorption: transport maximum

Maximum amount of a substance that can be reabsorbed
E.g. glucose exceeds its Tm it is lost in the urine

Tubular reabsorption: aldosterone

Influences reabsorption of water and sodium
In distal convoluted tubule Prevents

Tubular reabsorption: ADH

Affects permeability of the collecting duct to water
Reabsorb more water or increase water loss

Tubular secretion

Substances moved out of blood into the filtrate
Remove particular chemicals
Control ionic composition of the blood
Potassium - proximal and distal convoluted tubule in exchange for sodium

Urine chemical composition

Water Urea - breakdown of amino acids Sodium, potassium, phosphate, sulphate Creatine - metabolism in muscle tissue Uric acid - metabolism of nuclei acids

Regulation of urine concentration and volume

Body fluid osmotic concentration - 300mOsm Osmolality - number of solute particles in 1Kg Osmolarity - number of solute particles in 1L of water Counter current system Defending limb - water moves out into capillaries Ascending limb - impermeable to water, pumps salt out

Anti-diuretic hormone (ADH)

Plasma osmolarity detected by osmoreceptors in hypothalamus, tells posterior pituitary gland to increase or decrease ADH secretion Affects permeability of collecting duct

Increase of ADH

Collecting duct more permeable to water More aquaporin channels in membrane Greater water reabsorption Less urine More concentrated

Decrease of ADH

Collecting duct less permeable to water Less aquaporin channels in membrane Less water reabsorption More urine Less concentrated

Renin-angiotensin-aldosterone mechanism

Renin release from Juxtaglomerular apparatus - low pressure Converts angiotensinogen (inactive protein) into angiotensin I (inactive) then into angiotensin II by angiotensin converting enzyme (ACE)

Angiotensin II causes

Vasoconstriction of systemic blood vessels Release aldosterone from adrenal cortex - reabsorption of sodium and water in DCT Influences ADH release

Acid-bases balance

pH rage of blood - 7.35 - 7.45 More hydrogen ions - lower pH, more acidic More OH- ions - higher pH, more alkaline

Mechanisms to maintain the acid-base balance

Buffer - soak up excess H+ or OH- Respiratory system - H+ increase, respiratory rate increase, excess H+ breathed out as CO2 Renal system - low pH, H+ in urine

Production of erythropoietin

By kidneys Stimulates bone marrow to produce more red blood cells Hypoxaemia - low levels of oxygen in the blood, stimulates erythropoietin production

Calcium and phosphate regulation

Parathyroid hormone (PTH) Calcium reabsorbed and phosphate excreted Low plasma calcium - release PTH, increase calcium reabsorption from kidneys and GIT, release calcium from bones Needed for - strong bones and teeth, nerve impulse transmission, muscle contraction, blood clotting

Vitamin D metabolism

Obtained from sunlight Converted in the skin to form modified cholesterol Kidneys - converts vitamin D into the active form, stimulates absorption of calcium from GIT, maintain calcium levels