A. STRUCTURE AND FUNCTION OF KIDNEY Flashcards
what are the 2 main functions of the kidney
- excretion
- regulation
regulations of the kidney
- control of water and electrolyte (K+, Na+, Cl-) balance
- control of arterial blood pressure (through blood volume as increased blood volume = increased blood pressure)
- control of acid-base balance (H+, HCO3-) as kidney works with lungs to regulate fluid pH and kidney gets rid of excess ie - acid from metabolism
- endocrine: EPO, renin, 1,25-dihydroxyvitamin D3 (calcitriol), PGs
- glucose synthesis (gluconeogenesis) during prolonged fasting
what does the kidney excrete
- metabolic waste
urea (from amino acids)
creatinine (from creatine)
uric acid (from nucleic acid)
end products of haemoglobin breakdown (yellow)
hormone metabolites - foreign substances (drugs - metabolised or unmetabolised, pesticides, food additives)
what happens with kidney failure
disruption of homeostatic functions and we get severe abnormalities in body fluid volumes and composition
where do the kidneys sit
- paired bean-shaped organs
- lie in posterior wall of abdominal cavity and on either side of vertebral column
why is the right kidney lower than the left
due to liver positioning
size and weight of kidney
115-170g
11cm long by 6cm wide by 3cm thick
size of a clenched fist
what is the kidney surrounded by
tough protective fibrous renal capsule and visceral fat
(protects from mechanical trauma and shock)
what does the medial side of the kidney contain
a notch (helium) from which the renal artery, renal vein, nerves, pelvis and ureter pass through
what is the outer layer of kidney called
cortex
what is the inner layer of the kidney called
medulla
divided into multiple cone-shaped pyramids called nephrons (functional units of kidney)
what is the nephron
- functional unit of kidney
- 5 anatomical regions
how many nephrons is the kidney composed of
- 1 million
- we don’t make them
(age >40, natural loss of 10% per 10 years so by 70 we have 30% fewer functioning nephrons) - to see significant changes need 50% lost
what components does the nephron consist of
vascular (blood vessels) and tubular (nephron tube) components
blood supply to kidneys
blood flow to both kidneys is about 20-25% of total cardiac output (1.2L/min)
what are the 2 blood capillary beds
glomerular and peritubular capillaries
where do the afferent arterioles deliver blood to
glomerular capillaries (filtration occurs and this is the start of urine formation) and the glomerular capillaries rejoin to form efferent arterioles
what do the efferent arterioles do
- take unfiltered blood away from glomerulus
- they subdivide into peritubular capillaries and supply blood all around there kidney
difference in afferent and efferent arterioles
- efferent are smaller in diameter
- hence they receive blood with a relatively high hydrostatic pressure
what is the renal corpuscle made up of
Bowman’s capsule and the glomerulus
what are the glomerular capsules encapsulated in
Bowman’s capsule
collects filtered fluid from the capillaries
what is ultrafiltration
the start of urine formation as we are forcing a lot of fluid and solutes out of capillaries into Bowman’s space
where is the proximal convoluted tubule (PCT) and what is its main role
- continues from Bowman’s capsule
- lies entirely in cortex
- reabsorption back into blood
what cells are the PCT composed of
- single layer of cuboidal cells which interlock extensively, connected by tight junctions at their luminal surfaces
- microvilli present which increase the membrane SA
loop of henle
- forms a U-shape that dips into medulla
what is the Loop of Henle composed of
- thin descending limb which ends in the turn and plunges from cortex into the medulla
- thin ascending limb (only in nephrons with long Loops of Henle)
- thick ascending limb
what is the key role of the Loop of Henle
urine concentration
what is the macula densa
short segment of cells present at the end of the thick ascending limb of the loop of Henle
what is the juxtaglomerular apparatus composed of
- juxtaglomerular granular cells which secrete renin
- afferent and efferent arteriole
- macula densa (tubular cells)
what role does the juxtaglomerular apparatus
controlling nephron function
what is the appearance of the DCT
shorter and less convoluted than PCT
what is the role of the collecting duct
- DCT empties into the collecting duct
- each collecting duct may drain fluid from up to 8 separate nephrons
- ducts pass through the cortex and medulla to empty urine into the renal pelvis (ureter to bladder)
what 2 types of tubular cells are the late DCT and collecting duct made up of
- principal cells (P cells)
- intercalated cells (I cells) - smaller proportion
what role does I cells have
acid-base balance
what innervation of the kidney
- sympathetic nervous system (SNS)
- no PNS innervation
what effect does the SNS have on vascular smooth muscle: alpha-1 ARs
- noradrenaline is the NT released
- preferably afferent but also on efferent arterioles
- vasoconstriction which decreases blood flow and decreases GFR
what effect does the SNS have on juxtaglomerular (granular cells) of the juxtaglomerular apparatus: beta ARs
- stimulate renin secretion (angiotensin II formation - first part of RAAs)
what hormones act on the kidney
- vasopressin/ADH
- aldosterone
- parathyroid hormone
- natriuretic peptides
what hormones are produced by the kidney
- erythropoietin: only true hormone
- renin
- vitamin D3 (calciferol)
- prostaglandins
how does vasopressin/ADH work
- increases permeability of nephron to water
- leads to increased water reabsorption from filtrate into body so decreased water volume
*diuresis = production of urine
*anti-diuresis = less urine produced
how does aldosterone work
- part of RAAs
- increases sodium and hence water reabsorption
how does parathyroid hormone work
- plasma calcium homestasis
- increases calcium reabsorption from filtrate to plasma
how do natriuretic peptides work
- natriuresis is an increase in sodium excretion in urine followed by diuresis
- via inhibition of sodium reabsorption, suppression of RAAs
- vascular effects as well: vasodilation of afferent arteriole and vasoconstriction of efferent arteriole
how does EPO work
- stimulates RBC production
- proliferation and then differentiation of haematopoietic stem cells in bone marrow to mature RBCs
how does renin work
- part of RAAs
how does activated vitamin D3 work
- plasma calcium homeostasis
- increases plasma calcium
how does prostaglandins work
- paracrine effects
- vasodilation within renal corpuscle in particular and the pelvis causing increased blood flow and increased GFR
paracrine
- secretion within interstitial fluid that bathes cells
- travels short distance in IF (not blood) to affect neighbouring/adjacent cells
endocrine
- hormone produced by endocrine gland into blood
- travels to reach target cell tissue
what is the urinary system also known as
urinary tract or renal system
what does the urinary system consist of
kidneys
ureters
bladders
urethra
