Unit 8 Excretion

Excretion

-the process of removing metabolic wastes from the body

-one of the major ways the body maintains homeostasis

-Concentrated urine from the collecting tubule is transported to the renal pelvis

excretory system

large intestine

liver

skin

lungs

kidneys

Skin

-Excretes perspiration (a solution of water, salt, and some urea)

-Used to cool the body then secretion of wastes.

-Increase in wastes during times of renal failure (kidney)

Liver

-Breaks down old red blood cells.

-Yellow pigment in urine is also formed from the breakdown of heme from hemoglobin by the liver. It is then deposited in the blood and later removed by the kidneys

-excretion of bile pigments

Lungs

Expiration removes CO2 but it also results in the loss of water

-uses alveoli

Intestine

Certain salts, such as those of iron and calcium, are excreted directly into the cavity of the intestine by the epithelial cells lining it and become part of feces

Kidneys

-Excrete urine, which contains a combination of the end products of metabolism

-receive blood from the renal arteries

urinary system

Kidney - Produce Urine

Ureters - Transport Urine from the kidney to the Bladder

Bladder - Storage of Urine

Urethra - Elimination of Urine

nephron (function)

-Pressure filtration (at the glomerulus)

-Selective reabsorption (proximal convoluted tubule)

-Reabsorption of water (all along the nephron)

-Tubular excretion (at the distal convoluted tubule)

=Excretion of urine

Pressure Filtration

-Blood enters the Glomerulus which is surrounded by Bowman's capsule. Here blood pressure forces water, nutrients, and wastes out of the glomerulus and into Bowman's Capsule now called the filtrate. The liquid that collects in Bowman's capsule is plasma minus blood proteins. The deamination of amino acids by the liver produces ammonia which is then converted into urea, a major component of the waste pressure filtered into Bowman's Capsule.

Blood pressure is very important. If blood pressure is too low, filtration will not occur. A hormone called rennin is released from a specialized tissue in the Glomerulus that causes the constriction of the Glomerulus and thus, the blood pressure is increased to an adequate level.

Selective reabsorption

-Occurs mainly at the proximal convoluted tubule

-glucose, amino acids, vitamins, minerals, salt molecules and some water are reabsorbed into the peritubular capillary network

-Requires ATP

-The lower the pH of the blood the great the amount of bicarbonate ion reabsorbed.

Water Reabsorption

-The cells of the ascending loop of Henle actively pumps Na+ out of the nephron and K+ into the nephron

-Cl- follows the Na+ into the renal medula making the capillaries hypertonic to the nephron. As a result water follows the sodium and chlorine by osmosis (to even out electrical and concentration gradients).

-Water is reabsorbed along the entire length of the nephron. Hormones control the rate of ater reabsorption.

Tubular Excretion

-Occurs at the distal convoluted tubule

-Excess molecules in the blood, such as H+ ions, Histamine, Penicillin, creatine, and ammonia are secreted into the tubule from the blood, thereby helping to maintain homeostasis

-pH of blood is maintained by tubular excretion. If pH is too low, more hydrogen ions are secreted into the nephron

nephron (structure)

The cortex

-Bowman's Capsule

-Proximal Convoluted Tubule (PCT)

-Distal Convoluted Tubule (DCT)

The medulla (inner region)

-Loop of Henle - Both the cortex and medulla contain portions of the collecting ducts

-The Glomerulus.

-Peritubular capillary network

water entrance

-Drink Water

-Absorbed from food eaten

water exit

-Exhalation

-Urination

-Perspiration

-Tears (small amounts)

-Expectorating (phlegm)

-Defecation

PCT (proximal convoluted tubule)

reabsorbs amino acids, glucose, vitamins, mineral and salts as well as some water into the peritubular capillaries so that it is all reabsorbed by the end of the proximal tubule

DCT (distal convoluted tubule)

-third section of the nephron's tube system which transfers urine from the loop of Henle to the collecting ducts

-fine-tunes salt and water reabsorption

3 regions (kidney)

-Outer granulated region called the renal cortex.

-Striated or lined layer called the renal medulla.

-Inner cavity called the renal pelvis where urine collects

urine

-collects in the pelvic region of each kidney before being conducted by peristalsis through the ureters down to the urinary bladder

-When the urinary bladder becomes full, stretch receptor trigger urination, and the fluid is excreted via the urethra.

Renal Artery

-branches off aorta

-Brings blood to the kidney from heart to be ¨cleaned¨.

-High urea content

Renal Veins

-takes blood that leaves kidneys into IVC

-Return blood that is cleaned to the body.

-Low urea content, high glucose

ureter

tubes leading to the bladder from kidneys

Bladder

hollow organ with muscular walls that stores urine

glomerulus

-A ball of capillaries surrounded by Bowman's capsule in the nephron and serving as the site of filtration

-only allows vitamins and minerals to pass into tubule and reabsorbs any needed materials

Peritubular capillary network

capillary that surrounds a renal tubule and functions in reabsorption and secretion during urine formation

renal tubules

-make urine by removing waste, extra fluid, and other substances from the blood

-Urine moves through the renal tubules into the tubes that carry urine from the kidney to the bladder.

urine formation

-Pressure filtration (at the glomerulus)

-Selective reabsorption (proximal convoluted tubule)

-Reabsorption of water (all along the nephron)

-Tubular excretion (at the distal convoluted tubule)

-Excretion of urine

Renin

-hormone secreted by the kidney that raises blood pressure

-released from a specialized tissue in the Glomerulus that causes the constriction of the Glomerulus and thus, the blood pressure is increased to an adequate level.

filtrate

liquid filtered out of blood

Erythropoietin

a hormone secreted by the kidneys that increases the rate of production of red blood cells in response to falling levels of oxygen in the tissues.

ADH

-controls water absorption due to osmosis in the loop of Henle.

-increases permeability of the distal convoluted tubule and collecting duct so that more water can be reabsorbed

-If too little water is taken in orally the hypothalamus releases a hormone into the nerve tract to the posterior pituitary gland. The posterior pituitary gland releases ADH and more water is absorbed by the kidneys to maintain blood volume

-Alcohol sends a false message to the hypothalamus that there is too much water in the blood. ADH is not released, and therefore water is not reabsorbed and is lost in the urine. That is why if you drink alcohol, you urinate a lot and become dehydrated

how blood salt levels can influence blood volume and pressure

high blood salt levels create blood that is hypertonic to urine such that more water is reabsorbed into the blood, this increases blood volume which in turn increases blood pressure

Aldosterone

-controlled by adrenal cortex

-hormone which regulates the level of sodium and potassium in the blood

-If sodium is too low, aldosterone causes more sodium to be reabsorbed from the ascending limb of the loop of Henle into the renal medulla. If sodium concentration is too high the release of aldosterone is inhibited

-Increased sodium concentration causes the peritubular capillary network in the renal medulla to become hypertonic to the nephron. As a result more water is reabsorbed back into the blood from the descending limb of the Loop of Henle, the Distal Convoluted Tubule, and of course the collecting duct

medulla (renal pyramids)

involved in concentrating urine by salt and water reabsorption

renal cortex

part of the kidney where ultrafiltration occurs