Download The Urinary System

The Urinary System
Functions of the Kidneys
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Filter nearly 1200 ml of blood per minute
Return needed substances back to body
Regulate the volume and chemical makeup of
the blood (maintaining pH, water and salt
concentrations)
Production of renin and erythropoietin
Metabolizing vitamin D to its active form
Gross Anatomy
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Kidneys: two bean-shaped organs that filter
blood
Ureters: two tubes that drain urine away from
the kidneys
Urinary Bladder: stores urine until micturition
occurs; composed of transitional epithelium to
allow for stretching
Urethra: drains urine from bladder and
transports it outside; in females, only carries
urine; carries urine and semen in males
Gross Anatomy
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Two Kidneys
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Two Ureters
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Urinary Bladder
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Urethra
External Kidney Anatomy
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Located in a retroperitoneal position
Renal Hilus: region where ureters, renal blood
vessels, lymphatics, and nerves all join together
and exit/enter kidney
Connective Tissue Layers
 Renal
Capsule (prevents spread of infection)
 Adipose Capsule (fatty mass for shock absorbtion)
 Renal Fascia (outer layer that anchors kidney to
surrounding areas)
Internal Kidney Anatomy
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Renal Cortex
Renal Medulla
 With
renal pyramids
 Renal columns
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Renal Pelvis
 With
major calyces
and minor calyces
Arterial Blood Supply of the Kidney
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Renal Arteries
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Segmental arteries
Lobar arteries
Interlobar arteries
Arcuate arteries
Interlobular arteries
Afferent arterioles
Glomerular capillaries
Efferent arterioles
Peritubular capillaries
Venous Blood Supply of the Kidney
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Renal Veins
 Peritubular
venules
 Interlobular veins
 Arcuate veins
 Interlobar veins
 Renal vein
 Inferior vena cava
Nephron Anatomy and Structure
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Nephrons: functional unit of the kidney
Renal Corpuscle:
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Glomerulus (capillary bed made up of fenestrated capillaries for
filtration, allows filtrate to pass into the Bowman’s capsule)
Bowman’s Capsule (collection tubule surrounding glomerulus)
Three types of cells inside renal corpuscle:
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Juxtaglomerular cells (mechanoreceptors in afferent arteriole
sensing changes in BP, secrete renin)
Macula Densa cells (osmoreceptors responding to solute
concentrations and flow rate, vasoconstriction or vasodilation)
Mesangial cells (posses phagocytic and contractile abilities,
increase surface area for absorption)
Juxtaglomerular cells in the kidney respond to
changes in blood pressure and plasma sodium
concen. Decrease in either one will cause these
cells to make renin. Renin breaks down a
plasma protein called angiotensinogen which in
turn releases a substance called angiotensin-I.
Another enzyme, angiotensin –converting
enzyme; ACE, produced in the lungs converts
angiotensin-I to angiotensin –II which is carried
off in the blood.
When angiotensin-II reaches the adrenal cortex
it stimulates the release of aldosterone.
Angiotensin-II is also a powerful vasoconstrictor
used in regulating BP.
Renal Corpuscle
Nephron Anatomy and Structure
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Renal Tubule:
 Proximal
convoluted tubule (contain brush border
cuboidal epithelium for absorption and secretion in
the cortex)
 Loop of Henle (ascending and descending branches
in the medulla)
 Distal convoluted tubule (non-brush border cuboidal
epithelium cells, more secretion than absorption)
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Proximal/Distal refer to location relative to the
loop
Renal Tubule
Types of Nephrons
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Cortical: make up 85% of the nephron
content and found solely in the cortex
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Juxtamedullary: their loops of Henle dip
down into the medulla; associated with
vasa recta (regions where the efferent
arteriole does not break up into peritubular
capillaries)  produce concentrated urine
Renal Physiology
Occurs in Three Steps:
Non-selective filtration
Tubular reabsorption
Tubular secretion
Overview of Renal Physiology
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FILTRATION
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REABSORPTION
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SECRETION
Non-Selective Filtration
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(1) Unfiltered blood enters glomerulus via afferent
arteriole
(2) Inside the glomerulus, hydrostatic pressure is high,
pushing the filtrate (everything except proteins and blood
cells) into the Bowman’s capsule
(3) Efferent arterioles transport filtered blood to the
capillary beds
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Glomerulus unique because arterioles bring blood to the
capillary bed and take it away
Glomerular Filtration Rate: the amount of filtrate formed
in both kidneys per minute (125 mL/ min); majority is
reabsorbed in the renal tubule (124 mL)
Non-selective Filtration
Tubular Reabsorption
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Water, ions, and other substances reabsorbed into the blood via the
peritubular capillaries
Na+ moved out of tubule into the blood via facilitated diffusion
Glucose, amino acids, lactic acid, vitamins, and most cations
absorbed by secondary active transport (energy used from Na+/K+
pump)
Some ions (e.g. K+ and Cl-) move through the intercellular spaces
to leave the tubules in the interstitial spaces and then simply diffuse
out
Most substances (urea, some drugs, fat-soluble vitamins) diffuse
directly from the lumen of the tubules and into the peritubular
capillary network
98-99% of filtrate is reabsorbed
Tubular Reabsorption
Tubular Reabsorption
Tubular Secretion
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Involves the movement of substances out of blood
(peritubular capillaries) and into the filtrate
Substances can move by active or passive means
Substances commonly secreted: K+, H+, ammonia, byproducts of drugs and penicillin, and creatinine and
hormones
Final fluid draining from DCT into collecting ducts called
urine
Urine drains into renal pelvis and then merges into the
ureters and is sent by peristalsis to the bladder
Tubular Secretion
Regulation of Urine Volume
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(1) The descending limb of loop of Henle is
impermeable to solutes and permeable to water
(thus osmolarity increases)
(2) The ascending limb is permeable to solutes,
but not to water (thus osmolarity decreases)
(3) The collecting ducts in the deep medullary
regions are permeable to urea
Results in the concentration of urine
Effects of Hormones
on Urine Formation
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Antidiuretic hormone (ADH)
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Aldosterone
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Atrial natriuretic hormone (ANH)
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Renin and Angiotensin II
Urine Formation
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Urine composition
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90-95% water
Solutes constitute the other 5%
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Metabolic wastes (urea, uric acid, and creatinine)
Ions (Na+, K+, PO43-, SO42-, Ca2+, Mg2+)
Toxins and pigments (urochrome)
Hormones
Urine characteristics
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Yellow in color
Aromatic or ammonia
pH slightly acidic (can vary from 4.5 to 8.0)
Specific gravity 1.001 to 1.035
Abnormal Urine Constituents
Excretion and Micturition
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Bladder serves as a urine storage organ
Openings for both ureters and urethra located
on bladder interior (region bordered by these
three openings called the trigone)
Very distensible and can change shape to
accommodate for urine
Urethra conveys urine outside the body
Two sphincters (internal-involuntary and
external-voluntary) regulate urine flow outside
the body
The Bladder