Anatomy and Physiology of the Urinary System: Focus on the Kidneys, Slides of Zoology

Download Anatomy and Physiology of the Urinary System: Focus on the Kidneys and more Slides Zoology in PDF only on Docsity!

Essentials of Human Anatomy & Physiology

Unit 12:

The Urinary System

Organs of the Urinary system

∙ Kidneys (2)

∙ Ureters (2)

∙ Urinary bladder (1)

∙ Urethra (1)

Coverings of the Kidneys

∙ Adipose capsule

∙ Surrounds the kidney

∙ Provides protection to the kidney

∙ Helps keep the kidney in its correct location against

muscles of posterior trunk wall

∙ Ptosis-kidneys drop to a lower position due to rapid

fat loss, creating problems with the ureters.

∙ Ptosis can lead to hydronephrosis, a condition

where urine backs up the ureters and exerts

pressure on the kidney tissue.

∙ Renal capsule

∙ Surrounds each kidney

Regions of the Kidney

∙ Three regions of kidneys ∙ Renal cortex – outer region, forms an outer shell ∙ Renal columns – extensions of cortex- material inward ∙ Renal medulla – inside the cortex, contains medullary (renal) pyramids ∙ Medullary pyramids – triangular regions of tissue in the medulla, appear striated

∙ Renal pelvis – inner collecting tube, divides into major and minor calyces ∙ Calyces – cup-shaped structures enclosing the tips of the pyramids that collect and funnel urine towards the renal pelvis

Functions of the Urinary System

∙ Elimination of waste products

∙ filtering gallons of fluid from the bloodstream every day

creating “filtrate”

∙ “filtrate” includes: metabolic wastes, ionic salts, toxins, drugs

∙ Maintenance of blood

∙ Red blood cell production- by producing hormone

erythropoietin to stimulate RBC production in bone

marrow

∙ Blood pressure (vessel size)- by producing renin which

causes vasoconstriction

∙ Blood volume (water balance)- ADH released from

Anterior Pituitary targets the kidney to limit water loss

when blood pressure decreases or changes in blood

composition

∙ Blood composition (electrolyte balance)- water follows

salt; aldosterone reclaims sodium to the blood

∙ Blood pH- regulates H+ ions and HCO3- ions

Blood Flow in the Kidneys

∙ Rich blood supply to filter blood and adjust blood composition ∙ ~¼ of blood supply passes through the kidneys each minute ∙ Blood enters the kidneys under extremely high pressure ∙ Renal artery arises from abdominal aorta, divides into Segmental artery at hilus ∙ Inside renal pelvis, Segmental artery divides into Lobar artery, which branch into Interlobar artery travelling thru the renal column to reach the renal cortex ∙ At the medulla-cortex junction, the Interlobar artery curves over the medullary pyramids as the Arcuate artery. ∙ Small Interlobular arterioles branch off of the Arcuate artery and move away from the renal cortex and into the Nephron of the kidney

Nephrons

∙ The structural and functional units of the kidneys

∙ Over 1 million

∙ Responsible for forming urine

∙ Consist of renal corpuscle and renal tubule

∙ Renal corpuscle composed of a knot of capillaries

called the Glomerulus (a.k.a. Bowman’s Capsule)

∙ Renal tubule- enlarged, closed, cup-shaped end

giving rise to the PCT, dLOH, aLOH, DCT, and

CD.

Glomerulus

∙ Glomerular capillaries are covered with podocytes from the inner (visceral) layer of the glomerular capsule. ∙ Podocytes have long, branching processes called pedicels that intertwine with one another and cling to the glomerular capillaries. ∙ Filtration slits between the pedicels form a porous membrane around the glomerular capillaries. ∙ The glomerular capillaries sit within a glomerular capsule (Bowman’s capsule) ∙ Expansion of renal tubule ∙ Receives filtered fluid ∙ Renal tubule coils into the PCT, then the dLOH, aLOH, DCT and finally, the CD. ∙ Along the PCT, much of the filtrate is reclaimed

Renal Tubule

∙ Glomerular (Bowman’s) capsule enlarged beginning of renal tubule ∙ Proximal convoluted tubule- lumen surface (surface exposed to filtrate) is covered with dense microvilli to increase surface area. ∙ The descending limb of the nephron - Loop of Henle ∙ The ascending limb of the nephron coils tightly again into the distal convoluted tubule ∙ Many DCT’s merge in renal cortex to form a collecting duct ∙ Collecting ducts not a part of nephron ∙ Collecting ducts receive urine from nephrons and deliver it to the major calyx and renal pelvis. ∙ CD run downward through the medullary pyramids, giving them their striped appearance.

Blood Supply of a Nephron

∙ Peritubular capillary

∙ Efferent arteriole braches into a second capillary bed

∙ Blood under low pressure

∙ Capillaries adapted for reabsorption instead of filtration.

∙ Attached to a venule and eventually lead to the interlobular

veins to drain blood from the glomerulus

∙ Cling close to the renal tubule where they receive solutes and

water from the renal tubule cells as these substances from the

filtrate are reabsorbed into the blood.

∙ Juxtaglomerular apparatus

∙ At origin of the DCT it contacts afferent and efferent arterioles

∙ Epithelial cells of DCT narrow and densely packed, called

macula densa

∙ Together with smooth muscle cells, comprise the

juxtaglomerular apparatus

∙ Control renin secretion & indirectly, aldosterone secretion

Urine Formation Processes

∙ Filtration- Water & solutes

smaller than proteins are forced through the capillary walls and pores (of the glomerulus) into the renal tubule (Bowman’s capsule).

∙ Reabsorption- Water, glucose,

amino acids & needed ions are transported out of the filtrate into the peritubular capillary cells and then enter the capillary blood.

∙ Secretion- Hydrogen ions,

Potassium ions, creatinine & drugs are removed from the peritubular capillaries (blood) and secreted by the peritubular capillary cells into the filtrate.

Filtration

∙ Beginning step of urine formation

∙ Occurs at the glomerulus, nonselective passive process

∙ Water and solutes smaller than proteins are forced through

capillary walls of the glomerulus, which act as a filter.

∙ Fenestrations – (openings in glomerular walls) make

glomerulus more permeable than other arterioles.

∙ Podocytes cover capillaries, make membrane impermeable to

plasma proteins.

∙ Blood cells cannot pass

out to the capillaries; filtrate

is essentially blood plasma

w/o blood proteins, blood cells.

∙ Filtrate is collected in the

glomerular (Bowman’s) capsule

and leaves via the renal tubule