the urinary system. functions of the kidneys filter nearly 1200 ml of blood per minute return needed...
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The Urinary System
Functions of the Kidneys
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
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
Two Kidneys
Two Ureters
Urinary Bladder
Urethra
External Kidney Anatomy
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
Renal Cortex Renal Medulla
With renal pyramids Renal columns
Renal Pelvis With major calyces
and minor calyces
Arterial Blood Supply of the Kidney
Renal Arteries Segmental arteries Lobar arteries Interlobar arteries Arcuate arteries Interlobular arteries Afferent arterioles Glomerular capillaries Efferent arterioles Peritubular capillaries
Venous Blood Supply of the Kidney
Renal Veins Peritubular venules Interlobular veins Arcuate veins Interlobar veins Renal vein Inferior vena cava
Nephron Anatomy and Structure
Nephrons: functional unit of the kidney Renal Corpuscle:
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:
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
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)
Proximal/Distal refer to location relative to the loop
Renal Tubule
Types of Nephrons
Cortical: make up 85% of the nephron content and found solely in the cortex
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 filtrationTubular reabsorption
Tubular secretion
Overview of Renal Physiology
FILTRATION
REABSORPTION
SECRETION
Non-Selective Filtration
(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 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
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
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, by-
products 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
(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
Antidiuretic hormone (ADH)
Aldosterone
Atrial natriuretic hormone (ANH)
Renin and Angiotensin II
Urine Formation
Urine composition 90-95% water Solutes constitute the other 5%
Metabolic wastes (urea, uric acid, and creatinine) Ions (Na+, K+, PO4
3-, SO42-, Ca2+, Mg2+)
Toxins and pigments (urochrome) Hormones
Urine characteristics 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
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