chapter 25

transitional epithelium

line urianry tract; known as urothelium

nonkeratinized, stratified squamous

terminal portion of urethra

oliguria

Output below 500 mL/day may be caused by severe dehydration or renal disease

anuria

virtual absence of urine production

polyuria

Excessive urine production which may be due to diabetes mellitus or diabetes insipidu

presence of leukocytes

indicates UTI

cells

urine does not contain

ketones

byproducts of fat metabolism. Finding them in the urine suggests that the body is using fat as an energy source in preference to glucose; excessive amounts indicate diabetes, may also appear if there is severe deficiency of protein or carbohydrates in the diet

ketones and diabetes

In diabetes mellitus when there is not enough insulin (type I diabetes mellitus) or because of insulin resistance (type II diabetes mellitus), there is plenty of glucose, but without the action of insulin, the cells cannot take it up, so it remains in the bloodstream. Instead, the cells are forced to use fat as their energy source, and fat consumed at such a level produces excessive ketones as byproduct

urethra

only urologic organ that shows any significant anatomic difference between males and females; all other urine transport structures are identical. Males serve dual function for reproduction and urinary function while females only involves urinary function.

urinary bladder

collects urine from both ureters; lies anterior to uterus in females, posterior to the pubic bone and anterior to the rectum. bladder is a highly distensible organ comprised of irregular crisscrossing bands of smooth muscle, interior surface is made of transitional cellular epithelium that is structurally suited for the large volume fluctuations of the bladder. When empty, it resembles columnar epithelia, but when stretched, it "transitions" (hence the name) to a squamous appearance

detrusor muscle

irregular crisscrossing bands of smooth muscle that compose the urinary bladder

micturition

proper term for urination or voiding. It results from an interplay of involuntary and voluntary actions by the internal and external urethral sphincters. When bladder volume reaches about 150 mL, an urge to void is sensed but is easily overridden. Voluntary control of urination relies on consciously preventing relaxation of the external urethral sphincter to maintain urinary continence. As the bladder fills, subsequent urges become harder to ignore. Ultimately, voluntary constraint fails with resulting incontinence, which will occur as bladder volume approaches 300 to 400 m

urine passes through ureter

via peristalsis, contractions are generated by pacemaker cells in the renal pelvis and coordinated by the smooth muscle layers of the ureter. As urine is formed, it drains into the calyces of the kidney, which merge to form the funnel-shaped renal pelvis in the hilum of each kidney. The renal pelvis narrows to become the ureter of each kidney. As urine passes through the ureter, it does not passively drain into the bladder but rather is propelled by waves of peristalsis. As the ureters enter the pelvis, they sweep laterally, hugging the pelvic walls. As they approach the bladder, they turn medially and pierce the bladder wall obliquely. This is important because it creates an one-way valve (a physiological sphincter rather than an anatomical sphincter) that allows urine into the bladder but prevents reflux of urine from the bladder back into the ureter

renal blood flow in

renal artery -> segmental artery -> interlobar artery -> acrcurate artery -> interlobular artery -> afferent arteriole -> glomerulus

renal blood flow out

efferent arteriole -> peritubular capillaries -> interlobular vein -> arcurate veins -> interlobar veins -> renal vein

nephron

functional unit of kidneys, they cleanse the blood and balance the constituents of the circulation. Most in cortex. Contains an epithelial lined tubule, renal corpuscle composed of a bowman's capsule, glomerulus (cluster of capillaries), renal tubule, peritubular capillaries. 1 million nephrons.

urine formation

Goal of is to maintain homeostasis by regulating volume and composition of blood. Urine contains metabolic wastes and unneeded substances.

1. Filtration

2. Reabsorption

3. Secretion

loop of henle reabsorbs

H2O, NA, Cl into peritubular fluid

distal convulted tubule (DCT) reabsorbs

Na via aldosterone into blood in exchange for K+ into filtrate; Ca, Cl, secretes drugs, ions and toxins like K and H

proximal convuluted tubule (PCT) reabsorbs

water and sodium, all filtered glucose and amino acids, and a large percentage of bicarbonate. Other substances like potassium, calcium, and uric acid are also reabsorbed

ADH and aldosterone

affect collecting ducts of kidneys,

collecting ducts

regulate H2O and solute loss by: aldosterone and antidiuretic hormone (ADH)

aldosterone

plays role in reabsorption of Na (DCT and proximal part of collecting duct.

ADH

plays role in reabsorption of H2O (DCT and collecting duct), helps concentrate urine.

cells that make up renal corpuscle

glomerulus and Bowman's capsule

glomerulus

composed of fenestrated capillaries

cells of glomerulus

podcytes, endothelial cells, and glomerular mesangial cell

active renin

protein comprised of 304 amino acids that cleaves several amino acids from angiotensinogen (made by liver) to produce angiotensin I.

angiotensin I

not biologically active until converted to angiotensin II by angiotensin-converting enzyme (ACE) from the lungs.

Angiotensin II

a systemic vasoconstrictor that helps to regulate blood pressure by increasing it. also stimulates the release of the steroid hormone aldosterone from the adrenal cortex. Aldosterone stimulates Na+ reabsorption by the kidney, which also results in water retention and increased blood pressure. immediate and short-term effect of angiotensin II is to raise blood pressure by causing widespread vasoconstriction

renin-angiotensin-aldosterone interaction

kidneys cooperate with lungs, liver, and adrenal cortex through the renin-angiotensin-aldosterone system, Renin converts angiotensinogen (plasma protein from live) -> angiotensin I -> Angiotensin II at lung capillaries

Angiotensin II stimulates secretion of aldosterone (adrenal cortrex) & ADH (pituatoray) = increased GFR and BP

Aldosterone -Na+ reabsorption in DCT and collecting ducts, ADH H2O reabsorption in DCT

diuretic

agent that increases urine output; can increase water loss by interfering with the recapture of solutes and water from the forming urine. They are often prescribed to lower blood pressure. Coffee, tea, and alcoholic beverages are familiar diuretics