The Urinary System Flashcards
What is the function of renin, secreted by the kidneys?
This enzyme is involved in the activation of angiotensinogen
Six principal organs of the urinary system
- 2 kidneys
- 2 ureters
- urinary bladder
- urethra
What are the major functions of the kidneys?
- filter blood plasma
- regulate blood volume, pressure, and osmolarity
- electrolyte balance
- renin secretion
- erythropoietin secretion
- acid-base balance
- calcium homeostasis by participating in calcitrol synthesis
- detoxification
- support blood glucose levels during extreme starvation
What are nitrogenous wastes?
One of the most toxic metabolic wastes, consisting of urea (a byproduct of protein catabolism), uric acid, and creatinine
What is BUN?
- azotemia
- uremia
Blood urea nitrogen - measure of nitrogenous wastes in the blood
- Azotemia occurs when BUN is elevated
- Uremia is a dangerously high BUN that results in diarrhea, vomiting, dyspnea (SOB), cardiac arrhythmia, convulsions, coma, and death
What 4 organ systems carry out excretion?
(1) lungs
- CO2, other gases, water
(2) skin
- urea, salts, lactic acid, water
(3) digestive system
- salts, CO2, bile pigments, lipids, cholesterol, etc.
(4) kidneys
- metabolic wastes, drugs, hormones, etc
Purpose of the hilum of the kidney
Admits nerves, blood vessels, lymphatics, and the ureter
Three layers of connective tissue covering the kidney
(1) renal fascia - outermost
(2) perirenal fat capsule - adipose tissue
(3) fibrous capsule - protects kidney from trauma and infection
Two zones of renal parenchyma
(1) renal cortex
(2) renal medulla
Order of renal circulation
Aorta –> renal artery –> segmental arteries –> interlobar arteries –> arcuate arteries –> interlobular (cortical radiate) arteries –> afferent arterioles –> efferent arterioles –> peritubular capillaries –> interlobular veins –> arcuate veins –> interlobar veins –> renal vein –> inferior vena cava
**note there are no segmental veins
Renal medulla blood supply
Vasa recta – network of vessels stemming from efferent arterioles
Two principal parts of the nephron
(1) renal corpuscle
- filters blood plasma
(2) renal tubule
- coverts filtrate to urine
Components of the Renal Corpuscle
- Glomerulus
- Glomerular (Bowman) capsule
- outer layer is simple squamous
- inner layer has podocytes
**these components are separated by a filtrate-collecting capsular space
What are podocytes?
Cells in the visceral (inner) layer of the Bowman’s capsule that wrap around the capillaries of the glomerulus
Four main regions of the renal tubule
(1) proximal convoluted tubule (PCT)
(2) loop of Henle
(3) distal convoluted tubule (DCT)
(4) collecting duct (CD)
Proximal convoluted tubule (PCT)
- longest and most coiled
- simple cuboidal epithelium with prominent microvilli
- performs the greatest deal of absorption
Loop of Henle
- Thick and thin segments
- Thick segments = simple cuboidal to allow transport of salts
- Thin segments = simple squamous to be permeable to water
Distal convoluted tubule (DCT)
- simple cuboidal, no microvilli
- end of the nephron - contacts afferent and efferent arterioles
Collecting duct (CD)
- several DCTs drain into one CD
- simple cuboidal
- several CDs merge to form a papillary duct which drains into the minor calyx
Two types of nephron
(1) cortical nephrons
(2) juxtamedullary nephrons
Four stages of blood plasma to urine conversion
(1) glomerular filtration
(2) tubular reabsorption
(3) tubular secretion
(4) water conservation
Proteinuria (Albuminuria)
Hematuria
Can be causes by kidney infections or trauma to the filtration membrane
- albumin and blood are allowed to filter through
Glomerular filtration rate
- Amount of filtrate per minute for both kidneys
~180 L/day for males; ~150 for females
Three mechanisms controlling glomerular filtration
Three mechanisms of glomerular filtration:
(1) renal autoregulation
- ability of nephrons to adjust their own blood flow and GFR
(2) sympathetic control
- stress
- sympathetic fibers and adrenal epinephrine constrict afferent arterioles to slow urine production and redirect blood from kidneys to the heart, brain, and skeletal muscles
(3) renin
- drop in BP stimulates JG cells to secrete renin and raise BP via angiotensin pathway
Two mechanisms of renal autoregulation if GFR
(1) myogenic mechanism
- when BP rises, afferent arterioles constrict and efferent arterioles dilate to decrease blood flow
- opposite when BP drops
(2) tubuloglomerular feedback
- involves the juxtaglomerular apparatus
- macula densa, juxtaglomerular cells, and mesanglial cells
Macula densa cells of the juxtaglomerular apparatus
- epithelial cells at end of the loop on side facing arterioles
Juxtaglomerular cells of the juxtaglomerular apparatus
- Smooth muscle cells in the afferent arterioles (some in efferent)
- stimulated by macula densa cells to constrict or dilate the arterioles
- contain granules of renin released in response to low BP
Mesanglial cells of the juxtaglomerular apparatus
- in cleft between afferent and efferent arterioles
- among capillaries in glomerulus
- connected to macula densa and JG cells through gap junctions and communicated through paracrine secretions
- supportive matrix for glomerulus
- role in phagocytosis of debris
ACE inhibitors
Inhibit the angiotensin-converting enzyme in the lungs and kidneys that acts on angiotensin to create angiotensin II – ACE inhibitors are used to lower BP
Importance of sodium reabsorption during the tubular reabsorption step of urine formation
- Na reabsorption establishes an osmotic and electrical gradient that drives the reabsorption of water and other solutes
- other electrolytes, glucose, nitrogenous wastes, etc are also reabsorbed at this stage
Process of tubular secretion
Tubular secretion is a process where the renal tubule extracts chemicals from the capillary blood and secretes them into the tubular fluid for excretion
- this is why drugs must be taken in doses throughout day
Hormones regulating absorption by the DCT and CDs
- Aldosterone
- acts on thick segment of ascending limb of nephron loop, DCT, CD
- water retention to maintain blood volume and pressure
- Parathyroid hormone
- acts on PCT to stimulate P excretion
- acts on ascending limb of loop and DCT for Ca++ reabsorption
- raises [P] and lowers [Ca] in urine
- Atrial natriuretic peptide
- inhibits Na and water reabsorption to decrease BP
- ADH
- in response to dehydration and increased osmolarity, causes reabsorption of water by CD
Control of Timing of Micturition
- Spinal Micturition reflex (pons) is activated when bladder has ~200mL
- sensory signals travel from pelvic nerve to sacral spinal cord
- efferent signals travel back to bladder by way of pudenal (pelvic) nerve and PS ganglion
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