2.71-2.79B Excretory System

Excretion

Removal of metabolic waste and other useless/harmful material(s) from the body.

Metabolism

The chemical reactions that occur in cells and biological molecules.

Egestion

The removal of indigestible faeces (poo) from the alimentary canal.

Is egestion the same as excretion? Explain your answer.

Egestion is NOT the same as excretion, the faeces do NOT experience any chemical change/reaction, hence they’re NOT a metabolic product, but simply indigestible remains of food and bacteria/dead cells which is pushed out of the body.

What are the organs of excretion?

Lungs, kidney, and skin

The lungs excrete … from metabolic processes in the …/… system. The skin excretes … (…) containing the metabolic waste products of …, …, and …, for … and … The kidneys excrete … containing the metabolic waste products of …, …, and … to filter out blood

carbon dioxide, ventilation, respiratory, sweat, perspiration, urea, salts, excess water, thermoregulation, osmoregulation, urine, urea, excess water, salts

Urine

Fluid containing water, urea, and salts/ions. It’s produced in the kidneys, stored in the bladder, and removed through the urethra to eliminate metabolic wastes.

Adults produce about … of urine daily, this is the same as …, but the volume depends on how much … is drank and lost through other forms (e.g. …)

1\.5d㎥, 1.5L, water, sweating

1 … of urine contains about … of waste products and salts.

liter, 40g

Urea

Main nitrogenous excretory substance in humans produced by protein metabolism and chemical reactions from cellular metabolism. It’s filtered by the kidneys during urine formation.

Why is urea the product of __***protein***__ metabolism?

Carbohydrates and fats only contain carbon, hydrogen, and oxygen, while protein also contains nitrogen. Excess carbohydrates and fats can be stored as glycogen or subcutaneous/visceral fat. Excess proteins/amino acids cannot be stored, so amino acids are decomposed in the liver into carbohydrates (stored as glycogen), and urea, a nitrogenous (nitrogen-containing) waste product.

Homeostasis

Maintaining constant conditions of the body and its internal environment.

Osmoregulation

Process of maintaining water and salt/electrolyte concentrations (osmotic balance) across membranes within the body.

Internal environment

Surroundings of cells inside the body: blood and tissue fluid.

Tissue fluid

Aqueous solution of salts, glucose, and other solutes formed by leakage from blood capillaries. It is similar to blood plasma but lacks plasma proteins. Tissue fluid surrounds all cells, allowing transfer of nutrients between the blood and cells.

What happens if tissue fluid is hypertonic to cells?

Water travels from high water potential (cells) to low water potential (tissue fluid) by osmosis → cells lose water and become shrivelled/flaccid

What happens if tissue fluid is hypotonic to cells?

Water travels from high water potential (tissue fluid) to low water potential (cells) by osmosis → cells swell up and become turgid

Salts in the urine/blood are present as … For example, potassium (…), phosphate (…), ammonium (…), solution of sodium ions (…) and chloride ions (…) to form sodium chloride, etc. Excess … will be … from the blood.

ions, K +, HPO4 2-, NH4 +, Na +, Cl -, ions, removed

What (6 things) needs to be regulated in the body?

1. Temperature (thermoregulation)
2. CO2 (ventilation)
3. Blood sugar (blood glucose regulation)
4. Water (osmoregulation
5. pH
6. Urea (nephrons/excretory system)

Urinary system

Organ system that produces/excretes urine, osmoregulates, maintains electrolyte/salt balance, etc.

Renal artery

Artery branching from the aorta that supplies high pressure blood containing waste from the heart to kidneys.

Aorta

Main artery that carries blood away from the heart to the rest of the body.

Renal vein

Vein that carries deoxygenated, filtered blood from the kidneys and ureter to the inferior vena cava.

Inferior vena cava

Large vein that carries blood from the lower body to the heart’s right atrium.

Ureter

Tube carrying urine from the kidneys to the bladder.

Bladder

Hollow, muscular, sac-like organ that stores urine before its removal from the body.

Kidneys (and their 6 functions)

Bean-shaped, fist-sized organs located below the rib cage with one on each side of the spine that:


1. Filter blood
2. Remove metabolic waste
3. Osmoregulate
4. Form urine
5. Release vitamins/minerals
6. Secrete hormones/enzymes such as renin and erythropoietin.

Renin

Enzyme secreted and stored in the kidneys, it maintains/adjusts blood pressure by stimulating the production of angiotensin where necessary.

Angiotensin

Hormone that regulates blood pressure (by vasoconstriction to increase blood pressure), as well as triggering water and salt (sodium) intake.

Erythropoietin

Hormone which stimulates red blood cell production.

Urethra

Tube connecting bladder to the outside of the body, urine leaves the body through this tube.

Internal sphincter muscle

Upper sphincter muscle located at the opening of the bladder to the urethra. It’s made from smooth, involuntary muscle that automatically relaxes when the bladder is full.

External sphincter

Lower sphincter muscle surrounding the area of the urethra outside the bladder. It’s a skeletal, voluntary muscle that can contract to close the urethra and hold the urine, or relax to widen the urethra lumen and let urine pass through.

Why do babies urinate randomly without control?

Babies cannot control their voluntary sphincter → when their bladder is full, the involuntary internal sphincter muscle relaxes while the external sphincter muscle also involuntarily relaxes, releasing the urine. Toddlers learn to control the voluntary/external urethral sphincter and hold back urine as they grow older.

Each … is supplied with … by the …, branching off the ... Blood enters the kidneys at …, it’s filtered, “clean” blood then leaves the kidney through the … to the ... The kidney forms …, which leaves through the … to enter the ... When the … is full, the … relaxes to let urine enter the …. Once the … relaxes, urine can pass through the … and be … out the body.

kidney, blood, renal arteries, aorta, high pressure, renal vein, inferior vena cava, urine, ureter, bladder, bladder, internal sphincter muscle, excreted

Renal hilum

Point of entry of renal artery, exit of renal vein, exit of ureters, as well as the entry/exit of lymphatic vessels, nerves, etc, in the kidneys.

Renal artery

Artery that brings oxygenated, unfiltered blood to the kidneys. It branches off of the aorta.

Renal vein

Vein that brings deoxygenated, filtered blood (i.e. blood has no urea, but contains some salts and soluble wastes) away from the kidneys and into the inferior vena cava.

Renal pelvis

Area at the center of the kidney. It’s a funnel-like cavity structure where urine is collected whilst it’s produced. The renal pelvis is connected with the ureter, so it also helps carry urine to the bladder.

Ureter

Tube connecting urine from the kidneys to the bladder.

Calyx

Cup-like projection out of the renal pelvis. They’re the first parts of the renal pelvis and are where urine is collected/passes through before entering the renal pelvis. It includes the major and minor calyx.

Major calyx

Calyx surrounding apex of renal pyramids. Urine formed in the kidney passes through a papilla at the renal pyramid’s apex → minor calyx → major calyx → renal pelvis → ureter.

Minor calyx

Calyx that surrounds each renal pyramid’s renal papillae and collects urine from that pyramid. Several minor calyces converge to form a major calyx.

Renal cortex

Outer, red region of kidney containing arterioles of the renal artery and nephrons. Blood is first filtered here whilst it goes through the nephrons.

Renal medulla

Middle, dark region of the kidney that regulates urine concentration, blood’s water content, and blood’s salt content. Filtering tubes of nephrons are looped here, enabling selective reabsorption.

Renal pyramid (a.k.a. malpighian pyramid)

Conical sections of tissue that comprise the medulla and point towards the renal pelvis. Straight tubular structures and blood vessels → striated appearance.

Renal papilla

Apex of a renal pyramid that projects into a minor calyx’s cavity and through which nephrons’ collecting ducts discharge urine.

Renal column and its 4 functions

Connective tissue extensions that radiate downwards from the cortex through the medulla to


1. Separate renal pyramids
2. Divide kidney into 6-8 lobes
3. Provide supportive framework for vessels entering/exiting the cortex
4. Better anchor the renal cortex

Renal capsule

Fibrous connective tissue surrounding each kidney to support their soft tissue.

Nephron and its 3 functions

Kidney tubule, the functional unit of a kidney (around 1 million of these per kidney). It consists of a glomerulus, bowman’s capsule, proximal convoluted tubule, loop of Henle, distal convoluted tubule, and a collecting duct. Glomerular filtrate passes through the tubules before emerging as urine.


1. Filters blood
2. Selective reabosprtion of glucose, ions, amino acids
3. Excretion of urea, excess water, and salts, in urine

There are … associated with …, this elaborate … aids … as well as … of various substances

many blood vessels, nephrons, blood supply, ultrafiltration, selective reabsorption

Ultrafiltration

Filtration of the blood in the nephron’s glomerulus and bowman’s capsule, whereby the filtrate/semi-permeable membrane separates molecules of various sizes under pressure.

Selective reabsorption

Substances that are useful to the body (glucose, amino acids, some water, some minerals/ions and other small molecules) will be reabsorbed back into the blood.

Bowman’s capsule

Structure consisting of a hollow cup of cells at the start of a nephron/kidney tubule. It’s the site of ultrafiltration and encloses the Bowman’s space.

Adaptations of the Bowman’s capsule

The Bowman’s Capsule is 1-celled thick (very thin) → short distance → easy active transport, passive transport, or diffusion of glomerular filtrate to bowman’s space.

Bowman’s space

Beginning of the urinary space, continuous with the proximal convoluted tubule. It’s the cavity enclosed by/inside the Bowman’s capsule. This Bowman’s space surrounds the glomerulus as well and collects glomerular filtrate.

Glomerulus

Ball of capillaries surrounded by the Bowman’s Capsule at the start of the kidney tubule. It filters the blood, and produces glomerular filtrate.

Glomerular filtrate

Refers to the glucose, amino acids, H + (hydrogen) ions, bicarbonate ions, vitamins, water, urea, mineral salts, and other plasma solutes ultra-filtered into the bowman’s space.

Basement membrane

Membrane located between capillary walls of the glomerulus and walls of the Bowman’s capsule. It’s made from glycoproteins, type IV collagen, laminin, etc, but NOT cells.

The …, …, and … work together to filter ... They allow …, …, …, …, and … to pass through, but hold back … and large molecules like … (as these are too big to pass through … so they instead stay in the …).

glomerular capillary wall, basement membrane, bowman’s capsule, blood, water, urea, glucose, ions, small molecules, blood cells, proteins, capillary linings, blood

What happens after the glomerulus filters the blood?

The glomerular filtrate passes through into the Bowman’s space to be selectively reabsorbed or involved in urine formation, while the blood flows away from the nephron.

Afferent arteriole

Arteriole approaching and supplying blood to the glomerulus, they branch off the renal artery.

Efferent arteriole

Arteriole leaving the glomerulus, they branch into the renal vein.

Afferent arteriole blood pressure … Efferent arteriole blood pressure. Explain why.

>, efferent arteriole lumen diameter < afferent arteriole lumen diameter → afferent arteriole lumen is larger → more blood flows through afferent arteriole → more blood must flow into the efferent arteriole (smaller lumen diameter) after ultrafiltration at the glomerulus → higher blood pressure in glomerulus → glomerular filtrate is forced from the glomerulus into the bowman’s capsule/bowman’s space, this results in ultrafiltration due to blood pressure exertions.

… enters … through …, … leaves … through ... Waste products and … continues from … down to the … and continues to travel through the … to form ...

Unfiltered blood, nephron, afferent arteriole, filtered blood, nephron, efferent arteriole, glomerular filtrate, bowman’s space, proximal convoluted tubule, nephron, urine

Fill in the blanks on this table (top → bottom and left → right)

approaches/supplies blood to glomerulus, leaves/carries blood away from glomerulus, branches off renal artery, branches into renal vein, carries unfiltered blood containing nitrogenous waste (urea), carries filtered blood without nitrogenous waste (urea), wider, narrower, higher, lower, blood contains water/blood cells/platelets/glucose/amino acids/ions/nitrogenous wastes (urea), blood contains less water/glucose/amino acids/ions/nitrogenous wastes (urea), blood pressure, glomerular filtration rate

Proximal convoluted tubule and its 2 functions

Tubular segment of nephron that


1. Connects bowman’s capsule to descending limb of Henlé
2. Selective reabsorption of most or all of the glucose, some salts (sodium and chloride ions), some water, etc.

Descending limb of loop of Henlé

Part of loop of Henlé that descends (loops down) from the renal cortex into the renal medulla.

Thinner than ascending loop of Henlé.

Selective reabsorption of water, and salts (sodium and chloride ions).

Contains aquaporins.

Aquaporins

Proteins in cell membranes that selectively permit water to pass in out of cells by osmosis.

Ascending limb of loop of Henlé

Part of loop of Henlé that ascends (loops up) from the renal medulla to the renal cortex.

Comprised from a thin and thick segment.

Selective reabsorption of salt (sodium chloride, NaCl)

Loop of Henlé

Part of nephron forming a long loop into the renal medulla.

Selective reabsorption of water and salts into blood.

Concentrates fluid levels in nephron by reabsorbing more water.

Long loops of Henlé → … water reabsorbed → … water conserved → … solute concentration in … → … concentration of urine and … urine volume. Desert animals have … to help … more water.

more, more, high, urine, high, small, long loops of Henlé, conserve

Short loops of Henlé → … water reabsorbed → … water conserved → … solute concentration in … → … concentration of urine and … urine volume. Animals with easy access to water such as otters/beavers, have … as they do not need to worry about …, so their … is also more dilute and also … in volume.

less, less, low, urine, low, large, short, water scarcity, urine, high

Humans have a … of … and … loops of Henlé

mixture, short, long

Distal convoluted tubule and its 2 functions

Tubular segment of nephron that


1. Connects thick ascending limb of the loop of Henlé to collecting duct.
2. Selective reabsorption of more mineral salts such as NaCl (sodium chloride), HCO3 (bicarbonate), etc.

Collecting duct and its 4 functions

Last part of nephron where


1. Nephrons’ distal convoluted tubules join together and empty their remaining wastes into the collecting duct.
2. Some urea might be reabsorbed to maintain high medulla solute concentration so water can be reabsorbed from the hypotonic nephrons to hypertonic medulla by osmosis (with help from aquaporins and ADH).
3. Urine transported to renal pelvis and then to ureters by peristalsis.
4. Selective reabsorption of more water and some salts for osmoregulation.

Peritubular capillaries

Peritubular = Surrounded by a tubule.

Peritubular capillaries = Capillaries wrapping around nephron’s proximal and distal convoluted tubules to reabsorb what passes out of them and provide nutrients + oxygen to renal cortex.

Vasa recta

Tiny capillaries surrounding Henlé loops which provide nutrients + oxygen to renal medulla.

Summarize urine formation in the nephrons

1. Blood flows from aorta → renal artery → afferent arteriole
2. Unfiltered, high pressure blood flows from afferent arteriole → glomerulus → ultrafiltration → glomerular filtrate forced into Bowman’s space.
3. Small particles (e.g. glucose, electrolytes, urea, water, mineral salts, and other plasma solutes) diffuse (or actively transport) through past the capillary wall, basement membrane, and Bowman’s capsule into the Bowman’s space while large particles (e.g. blood cells and proteins) cannot fit through the capillary linings so stay in the blood and are not filtered out of it.
4. Clean, filtered blood which does not contain any urea leaves the glomerulus through the efferent arteriole → renal vein → inferior vena cava.
5. Glomerular filtrate, water, and waste travels through the Bowman’s capsule’s Bowman’s space and continues its journey through the nephron’s tubular structure to form urine.
6. All/most glucose, some salt, and some water is selectively reabsorbed back into the proximal convoluted tubule, which is wrapped around by peritubular capillaries. Selective reabsorption of glucose happens by active transport, the nephron is adapted for this by having many mitochondria to provide energy for the active transport of glucose molecules. Reabsorption of glucose cannot take place anywhere else in the nephron as the gates that facilitate the active transport of glucose are only found in the proximal convoluted tubule.
7. Selective reabsorption of water and salts from urine occurs in the descending limb of the loop of Henlé. Water is reabsorbed by osmosis through aquaporins because the filtrate is hypotonic to insterstitial fluid → water travels from filtrate (high water potential) to interstitial fluid (low water potential) → Urine becomes concentrated due to water reabsorption from descending limb of Henlé → lots of salts in less water (high solute concentration).
8. Ascending limb of Henlé → Selective reabsorption of salt occurs → regulate solute concentrations; no aquaporins → prevents water from going from the interstitial fluid (hypotonic) to nephron’s filtrate (hypertonic).
9. Products of selective reabsorption from the loop of Henlé are reabsorbed back through the vasa recta.
10. Distal convoluted tubule → selective reabsorption of more mineral salts into the peritubular arteries
11. During selective reabsorption, all the filtered glucose, as much water as necessary to maintain constant blood plasma water levels, and as much ions as necessary to maintain mineral ion balance in the blood plasma, is reabsorbed back into the blood.
12. The distal convoluted tubule of multiple nephrons connect at the collecting duct.
13. The collecting duct brings urine to the tip of a renal pyramid, which transports urine into the renal papilla → minor calyx → major calyx → renal pelvis → ureter → bladder → urethra. More water and some salts may also be selectively reabsorbed back into the blood at the collecting duct.
14. Final urine has much higher urea concentrations than in the blood, it also has controlled quantities of water and ions for osmoregulation. Some substances may also be secreted into the nephron.

Interstitial fluid and its 2 functions

Fluid surrounding cells coming from substances that leak out capillaries.


1. Brings oxygen + nutrients to cells
2. Removes waste products from cells.

Amount excreted formula

Amount excreted = Amount filtered + Amount secreted - Amount reabsorbed

…, … blood enters the … through the ... The … branches into smaller … until the … reaches … in the ... Blood is filtered and leaves the … as well as … via the ... After blood filtration has occurred, … are collected in the … Waste flows from the … through the …, to the …, through the …, through the …, into the …, …, …, before exiting the body by … via the ...

Deoxygenated, unfiltered, kidneys, renal artery, renal artery, arterioles, blood, nephrons, renal cortex, nephrons, kidneys, renal vein, waste products, nephrons’ collecting ducts, collecting duct, renal medulla’s renal pyramids, renal papilla, minor calyx, major calyx, renal pelvis, ureter, bladder, excretion, urethra

Adrenal glands and its 4 functions

Small, triangular-shaped glands located on top of each kidney. Regulates …


1. Metabolism
2. Immune system
3. Blood pressure
4. Stress response, and other essential functions.

Hypothalamus and its 3 functions

Region in brain that


1. Controls body temperature, hunger, and thirst.
2. Signals/regulates the production of homeostatic hormones.
3. Detects water and solute concentrations in the blood.

Pituitary gland

Pea-sized gland at base of brain that regulates growth, metabolism, and reproduction by secreting hormones.

Diuresis

Increased excretion of urine. Diuretics = substances that promote diuresis.

Antidiuresis

Reduced/suppressed excretion of urine.

Antidiuretic hormone (ADH)

Hormone released from pituitary gland. It controls blood water concentration increasing water reabsorption from collecting ducts → less urine excreted

What happens when there is low water concentration in the blood?

Low water concentration in blood → high solute concentration in blood → hypothalamus’ receptor cells detects high solute concentration in blood → hypothalamus creates feelings of thirst so person drinks more water and pituitary gland releases more ADH → More ADH travels to kidneys via bloodstream → collecting ducts become more permeable to water → more water is reabsorbed back into the blood by osmosis → higher urine concentration and lower urine volume so blood becomes more dilute and body loses less water.

What happens when there is high water concentration in the blood?

High water concentration in blood → low solute concentration in blood → pituitary gland releases less ADH → less ADH travels to kidneys via bloodstream → collecting ducts become less permeable to water → less water is reabsorbed back into the blood by osmosis → lower urine concentration and higher urine volume so blood becomes more concentrated and body loses more water so high water concentrations in the blood return to a normal level.

Negative feedback

Homeostatic process where change in body is detected and body responds by doing things opposite to that change to reverse its effects and return bodily conditions to their optimum/normal. For instance, osmoregulation by ADH is a negative feedback loop.

Positive feedback

Process whereby change in body is detected and the body response by doing things to encourage/maximize that change to make bodily conditions closer to their optimum/normal by homeostasis. For instance, increased release of oxytocin during labour is a positive feedback loop.

Oxytocin

Hormone released by pituitary gland that increases uterine contractions (→increased pressure on cervix in labour), and stimulates milk ejection into breast ducts.

Cervix

Lower, narrow end of uterus forming a canal between the uterus and vagina.

Nephrotic syndrome

Life-threatening condition causing kidneys to leak lots of protein into the urine, due to impaired glomeruli (→ impaired ultrafiltration). Nephrotic syndrome can only be treated by a dialysis machine until kidney transplants occurs.

Diabetes’ effect on the kidneys/urine

Damages blood vessels in kidneys as well as glomeruli → Kidney damage + High blood pressure, etc.

Impaired blood glucose regulation → excess glucose in blood → excreted through urine → presence of glucose in urine when there shouldn’t be.

Kidney dialysis

Clinical procedure to remove metabolic waste products + excess fluid from blood when kidneys are damaged, to osmoregulate and regulate blood pressure.

Hemodialysis

Dialysis machine + special filter (artificial kidney/dialyzer) cleans your blood.

Hemodialysis procedures.

1. 2 needles are inserted into your arm.
2. Each needle is connected to a flexible plastic tube connected to a dialyzer.
3. Roller pumps move along and compress tubing connecting the patient’s blood to the dialyzer, this produces continuous blood flow and helps push blood through to the dialyzer.
4. Dialysate is the fluid added into, and that passes through, the dialyser during dialysis. It’s composed form water, electrolytes, as well as salts, and is almost completely isotonic to the patient’s blood to aid osmoregulation.
5. In the dialyser, partially permeable membranes surround tubes containing the blood, whilst dialysate is added to surround the tubes. Small molecules and waste products from the blood diffuse through the partially permeable membrane (larger molecules like blood cells and proteins stay in the blood) through to the dialysate, which then exits/leaves the dialyser.
6. The filtered blood then leaves the dialyser through a tube, and returns to the patient’s body through the second tube. Along the way, there is a filter and bubble trap to stop air bubbles from getting into the patient’s blood system.

Dialyzer

External filter machine that cleans your blood when your kidneys are damaged.