ALHT106 Lecture 3: Lecture 3
Structures/ Organs of the Urinary system:
Kidneys:
2x kidneys- produces urine
Urinary tract (organs that eliminate urine):
2x uterus (1 from each kidney)- transports urine from
kidneys to bladder
1x urinary bladder (muscular sac)- temporarily stores
urine prior to elimination
1x urethra (exit tube)- conducts urine to exterior; in
males, transports semen as well
Kidney location:
Retroperitoneal- T12 to L3- superior lumbar of posterior
abdominal wall
Adrenal glands lie superior to each kidney
Kidney physiology (functions):
-Water balance (water homeostasis) and blood/plasma volume
-Maintains ECF osmolarity and concentration of most ECF ions (e.g. Na+, K+, Cl-, H+, HCO3-)
-Acid-base balance (pH maintenance)- loss of H+ and HCO3- in urine
-Calcium regulation (activation of vitamin D to active hormone calcitriol)
-Blood pressure maintenance (Renin production) which maintains kidney function
-Anaemia correction (secretion of EPO in response to reduced renal O2 levels and a drop in rbc
numbers)
-Protein catabolism (for gluconeogenesis in BGL homeostasis)
-Excretion- filtration and removal of toxins (drugs, metabolic waste e.g. urea, uric acid, creatine,
bile pigment)
Maintenance of the composition of the extracellular fluid: ECF volume, electrolyte composition and
osmolarity. Therefore the major function of the kidney is HOMEOSTATIC REGULATION. Also,
kidneys are the main route for eliminating potentially toxic metabolites and foreign compounds from
the body (min 500mL urine/day)
The Nephron:
-each nephron has tubular (filtrate) components and vascular (blood) components
-Tubular components = long tubular passage
-Bowman’s capsule proximal convoluted tubule PCT loop Henle distal convoluted tubule DCT
collecting duct CD
Vascular components:
-On entering the kidney, renal artery subdivides eventually forming many afferent arterioles… into
the glomerulus
-Glomerulus is a tuft of capillaries where filtration occurs- filtrate formed is almost identical to
plasma then passes through tubular components
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-the kidneys receive 25% of total cardiac output (1,200ml/min) through the renal retry (from
abdominal aorta)
1. Renal artery segments an radiates eventually forming the afferent arterioles in the ‘glomerulus’
2. Blood filtered
3. Blood leaves glomerulus in efferent arterioles
4. Peritubular capillaries
5. Re-segment forming
6. Renal vein
Peritubular capillaries are a mesh that are draped over the tubules secreting and reabsorbing
substances to and from the filtrate. Capillaries are continuous with the efferent arteriole
-Renal nerves innervate individual nephrons
-This SymNS innervation adjusts rates of urine formation by:
1. Altering blood flow and pressure at the afferent and efferent arterioles
2. Stimulates renin release from JG apparatus in affront arteriole ( > promotes ADH &
aldosterone)
Kidney anatomy and physiology:
Tubular components of the nephron
Bowman’s capsule- cup shape that collect glomerular filtrate from blood
Proximal tubule- reabsorption and secretion of substances from peritubular capillaries
Loop of Henle- osmotic gradient produced for filtrate concentration
Distal tubule meets the afferent and efferent arterioles at the juxtaglomerular apparatus- helps to
regulate kidney function
Distal tubule and collecting duct- variable, controlled reabsorption and secretion of substances
Kidney physiology: the main processes:
There are three basic processes:
1. Glomerular filtration
-20% of plasma that enters the glomerulus is filtered
-water and most solutes in blood plasma move into renal tubule (PCT)
-filtrate and plasma have the same osmolarity and composition except
-cells and most large proteins do not get filtered in health
2. Tubular reabsorption
-as filtrate flows along tubules, tubule cells reabsorb water and other useful substances
-returned to venous system via peritubular capillaries
3. Tubular secretion
-selective transfer of substances from the peritubular capillaries into the renal tubule lumen (e.g.
wastes, H+, ammonium, urea, drugs etc)
-provides a second route for substances to enter renal tubules from the blood
Review:
Glomerular filtration- filtration of a protein-free plasma from the glomerulus
Tubular reabsorption- selective movement of filtered substances from the tubular lumen into
peritubular capillaries
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Tubular secretion- selective movement of non-filtered substances from peritubular capillaries to
tubular lumen
Hormones control final urine composition:
Amount of water and solute reabsorption and excretion depend on the body’s needs…
Four main hormones involved in the DCT and collecting ducts:
-Aldosterone, angiotensin II, antidiuretic hormone (ADH), parathyroid hormone (PTH)
-Aldosterone, ADH, and AgII are all involved with Na+, K+, H+ or water balance
-PTH increases Ca reabsorption from the DCT
Urinary tract:
Urine passes along the CD through renal pelvis, to uterus and then to urinary bladder for storage
until elimination via urethra
Uterus:
Muscular tubes that use peristalsis to move urine to bladder
Bladder:
Hollow, muscular distensible organ in pelvic cavity stores urine before voiding
Urethra- male and female:
Exit tube from body;
Female- 4cm, passage of urine only
Male- 20cm, passage of semen and urine
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Document Summary
2x uterus (1 from each kidney)- transports urine from kidneys to bladder. 1x urinary bladder (muscular sac)- temporarily stores urine prior to elimination. 1x urethra (exit tube)- conducts urine to exterior; in males, transports semen as well. Retroperitoneal- t12 to l3- superior lumbar of posterior abdominal wall. Water balance (water homeostasis) and blood/plasma volume. Maintains ecf osmolarity and concentration of most ecf ions (e. g. na+, k+, cl-, h+, hco3-) Acid-base balance (ph maintenance)- loss of h+ and hco3- in urine. Calcium regulation (activation of vitamin d to active hormone calcitriol) Blood pressure maintenance (renin production) which maintains kidney function. Anaemia correction (secretion of epo in response to reduced renal o2 levels and a drop in rbc numbers) Protein catabolism (for gluconeogenesis in bgl homeostasis) Excretion- ltration and removal of toxins (drugs, metabolic waste e. g. urea, uric acid, creatine, bile pigment) Maintenance of the composition of the extracellular uid: ecf volume, electrolyte composition and osmolarity.
