Biology 322 Human Anatomy I Renal System

Renal (Urinary) System Primary function: Maintains homeostasis by regulating concentrations of both water and solutes in the blood. Disposes of metabolic wastes excess water excess ions toxins while retaining proper amounts of water proper concentrations of ions nutrients anything else needed in blood Secondary function: Regulates blood pressure within normal range (homeostasis)

Organs of Renal System

Kidney Located high in abdominal cavity Posterior to peritoneum Liver pushes right kidney more inferiorly Mass ~ 150g Size ~ 12 cm x 6 cm x 3 cm Lateral surface convex Medial surface concave with hilus where renal artery, renal vein, ureter connect

Kidney Capsule: External covering of dense irregular connective tissue Cortex: Outer solid region Medulla: Inner solid region 8 to 12 cone-shaped masses (apex toward hilus) called renal pyramids, separated by renal columns Pelvis: Hollow medial region, extensions = calyces Connects medially with ureter

Kidney: Each renal artery (direct branch of aorta) divides into lobar or segmental arteries, which divide into interlobar arteries, then arcuate arteries (between cortex & medulla), which give off interlobular arteries (Saladin may call these “cortical radiate arteries” into both cortex & medulla.

In cortex, interlobular arteries send blood through afferent arterioles into groups of capillaries called glomeruli. This is where filtration will occur to begin formation of urine From a glomerulus, blood flows out an efferent arteriole to another set of capillaries called peritubular capillaries which surround the tubules where urine is forming.

Each renal artery divides into lobar arteries, interlobar arteries, arcuate arteries, interlobular arteries, afferent arterioles, glomeruli, efferent arterioles, peritubular capillaries Blood then flows into interlobular veins or arcuate veins, interlobar veins, and lobar veins to reach the renal vein which carries it to the inferior vena cava.

Let’s go back to the glomerulus: Consists of a group of interconnected capillaries. As blood flows through these capillaries, plasma (the liquid part of blood) is filtered out and flows though a series of tubes to form urine. This series of tubes is called a nephron.

Structure of Glomerulus Capillary wall (simple squamous epithelium, fenestrated) plus podocytes plus basement membrane between them form the filtration membrane across which liquid is filtered from the blood to the glomerular capsule.

Distal Convoluted Tubule Glomerular (Bowman’s) Capsule Proximal Convoluted Tubule Collecting Duct Loop of Henle

Each kidney contains ~ 1,000,000 nephrons Pattern of nephrons creates pattern of cortex and medulla: Cortex consists primarily of convoluted tubules which twist many directions. Medulla consists primarily of loops of Henle & collecting ducts all oriented in the same direction

This fluid filtered out of the blood flows into the proximal convoluted tubule, through other parts of nephron, into collecting duct. Recall that nephron is surrounded by peritubular capillaries for resabsorption of water and solutes

Urine passes from a collecting duct into a minor calyx, then a major calyx, then the pelvis of the kidney.

Urine leaving the pelvis enters the ureter, which carries it to the urinary bladder.

Ureters: Retroperitoneal. Anterior to common iliac arteries & veins. Deliver urine to posterolateral parts of urinary bladder.

Ureter: Mucosa: Transitional epithelium Lamina Propria (loose C.T.) Muscularis: Thick wall of smooth muscle Adventitia: Dense irregular C.T.

Urinary Bladder: In pelvis, posterior to pubic bone Superior surface covered by peritoneum Female: Anterior to uterus/vagina Male: Anterior to rectum Superior to prostate

Urinary Bladder: Mucosa: Transitional epithelium Lamina propria Muscularis: Thick smooth muscle (“detrusor”) Adventitia (C.T.) covers most of bladder Serosa on its superior surface

Urinary Bladder: Muscularis (detrusor muscle) and Internal Urethral Sphinter both smooth muscle; thus involuntary Urine leaving bladder enters urethra

Urethra: Adventitia: Dense irregular C.T. Muscularis: Thick wall of smooth muscle Mucosa: Epithelium varies from transitional near bladder to stratified squamous at end Male urethra much longer, has middle region of stratified columnar. Female urethra does not. Lamina Propria (loose C.T.)

External Urethral Sphincter External Urethral Meatus

Tonight: On yourself or another person, locate kidneys ureters bladder urethra