1. The Urinary System

2. 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

3. 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

4. Gross Anatomy
Two Kidneys
Two Ureters
Urinary Bladder
Urethra

5. 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)

6. Internal Kidney Anatomy
Renal Cortex
Renal Medulla
With renal pyramids
Renal columns
Renal Pelvis
With major calyces and minor calyces

9. 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

10. Venous Blood Supply of the Kidney
Renal Veins
Peritubular venules
Interlobular veins
Arcuate veins
Interlobar veins
Renal vein
Inferior vena cava

11. 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)

12. 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.

13. Renal Corpuscle

14. 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

15. Renal Tubule

16. 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

17. Non-selective filtration
Renal Physiology
Occurs in Three Steps:
Non-selective filtration
Tubular reabsorption
Tubular secretion

18. Overview of Renal Physiology
FILTRATION
REABSORPTION
SECRETION

19. 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)

20. Non-selective Filtration

21. 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

23. Tubular Reabsorption

24. Tubular Reabsorption

25. 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

26. Tubular Secretion

27. 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

28. Effects of Hormones on Urine Formation
Antidiuretic hormone (ADH)
Aldosterone
Atrial natriuretic hormone (ANH)
Renin and Angiotensin II

29. Urine Formation Urine composition Urine characteristics 90-95% water
Solutes constitute the other 5%
Metabolic wastes (urea, uric acid, and creatinine)
Ions (Na+, K+, PO43-, 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 to 1.035

30. Abnormal Urine Constituents

31. 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

32. The Bladder