10.2Chapter 10: Excretion in Humans

The human excretory system — Alhussan Biology - Stage 9 Revision Notes & Topical Questions

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10.2 The human excretory system — Kidneys, Ureters, Bladder and Urethra — Alhussan International Academy — Biology (Stages 7–9) notes: Name and locate the parts of the human excretory (renal) system, describe their functions and outline how urine is made and stored.Human excretor…

Human excretory system (renal system)
Renal artery
Renal vein
Blood flow
Rich blood supply
Filtration

Part 1 of 5The urinary system

The urinary system

Human excretory system (renal system)

Human excretory system (renal system) it removes urea and controls water balance, and urine flows through its parts in a set order.

Kidneys

Kidneys two organs at the back of the abdomen, protected by the lower ribs, which filter the blood and make urine.

Ureters

Ureters two narrow tubes that carry urine from the kidneys to the bladder by waves of muscle contraction.

Bladder

Bladder a muscular, stretchy bag that stores urine and is emptied when it is full.

Urethra

Urethra the tube through which urine leaves the body, with a ring of muscle (sphincter) controlling release.

Part 2 of 5Blood supply and kidney structure

1Renal artery

Renal artery it brings blood containing urea from the liver to the kidney.

2Renal vein

Renal vein it carries away blood with much less urea.

3Blood flow

Blood flow kidneys receive about one fifth of the blood pumped by the heart, which shows how important their work is.

4Regions

Regions the cortex is where filtration takes place, the medulla is where water is reabsorbed, and the pelvis collects urine and leads to the ureter.

Part 3 of 5How the kidneys make urine

Rich blood supply

Rich blood supply the blood entering carries dissolved food molecules, oxygen, salt, urea and many other substances.

Filtration

Filtration water, glucose, salts and urea pass out of the blood at the glomerulus.
Blood cells and big molecules the body needs stay in the blood.

Selective reabsorption

Selective reabsorption useful small molecules,
- including all the glucose, most of the water and the salts the body needs, are taken back into the blood in the tubule.

Urine

Urine the remaining liquid, containing urea, excess water and salts, passes to the collecting duct as the yellow liquid urine.

Volume

Volume an average adult produces about 1500 cm³ of urine every day.

Part 4 of 5Controlling water balance

1Large drink

Large drink the kidneys filter a lot of water out of the blood, so lots of very dilute urine is produced.

2Little drink, hot weather or exercise

Little drink, hot weather or exercise the kidneys save water to keep the blood at the right concentration,
- so a small volume of concentrated, darker urine is produced.

3ADH

ADH the hormone ADH, released from the pituitary gland in response to blood concentration, adjusts how much water is reabsorbed.

4Urine colour

Urine colour it varies from very pale to deep yellow, and pale yellow usually means the body is well hydrated.

Part 5 of 5Urine composition and health

Substance	In blood entering kidney	In urine
Urea	Present	Higher concentration
Glucose	Present	None (in a healthy person)
Protein	Present	None
Water	Present	Varies with need

Urine tests
- doctors check urine samples to make sure patients have healthy kidneys.
- Glucose in urine suggests diabetes.
- Protein in urine suggests kidney damage.

Key terms

Term	Meaning
Kidney	An organ that filters the blood and makes urine.
Ureter	A tube carrying urine from a kidney to the bladder.
Bladder	A muscular bag that stores urine.
Urethra	The tube through which urine leaves the body.
Renal	Relating to the kidneys.
Selective reabsorption	Taking useful substances back into the blood from the filtrate.