[BIO] Chapter 9 - Excretion in Humans

© Hee Xin Wei (Copyrighted) Topic 9: Excretion in Humans

Chapter Analysis FOCUS EXAM WEIGHTAGE •Constitute to around 5% in Paper 2 in the past 5 years •commonly tested in MCQ and structured questions •tested twice in section B in the past 5 years •straightforward chapter •linked to homeostasis & hormones

Excretion Human Urinary System Kidney and Nephron Key Concept

Excretion •Excretion is the process by which the body removes metabolic waste products and toxic materials. •Important process because metabolic waste products can be harmful to the body if they are not removed and accumulate in the body •Metabolic processes consist of both anabolic process and catabolic process Anabolic: reaction that build small molecules to complex molecules -Condensation reaction eg synthesis of proteins from amino acids, synthesis of glycogen from glucose, synthesis of lipid from fatty acids and glycerol -Photosynthesis Catabolic: reaction that break down complex molecule to smaller molecules -Hydrolysis reaction eg digestion of food substance -Respiration -Deamination of amino acids Excretory organs Metabolic waste productsExcretion Lungs Carbon Dioxide Exhaled air Kidneys Excess mineral salts, urea and excess water Urine Skin Excess mineral salts, small amount of urea and excess water Sweat Liver Bile pigments Secreted as bile, excreted as part of faeces Leaves Oxygen Diffuse out of leaf

human urinary system kidney •two bean-shaped organs •unit of kidney is nephron ureters Tube that connects the kidney to the urinary bladder bladder •an elastic organ that collects and stores urine excreted by the kidneys. •sphincter muscle at the base of the bladder controls the flow of urine into the urethra, which is controlled by nervous impulses from the brain. urethra Tube that connects bladder to outside of body

structure of kidney cortex The outer region of kidney, covered by protective fibrous renal capsule medulla The inner region of kidney consisting of a number of renal pyramids/conical pyramids renal pyramid •conical structures consisting of nephrons, which are the urine-producing units of the kidney. •empty urine into the renal pelvis, which will collect urine from all the pyramids to deliver to the ureter renal pelvis Enlarged portion of ureter renal artery and renal vein Blood enters each kidney from the renal artery and leaves via the renal vein

structure of nephron Nephron functional unit of kidney, responsible of urine formation renal corpuscle (malpighian corpuscle) consists of both bowman capsule and glomerulus glomerulus A ball of capillaries start from wider afferent arteriole and drains into a narrower efferent arteriole. bowman’s capsuleSurrounds the glomerulus in a cup-like structure path of blood renal artery —> afferent arterioles —> efferent arterioles —> capillaries —> venues —> renal vein proximal convoluted tubule •responsible for selective reabsorption of water, mineral salts, glucose and amino acid •contain many mitochondria loop of henlé distal convoluted tubule

urine formation osmoregulation kidney dialysis Key Concept

urine formation ultra filtration Ultra filtration 1.Blood flows from renal artery and enters the glomerulus through afferent arteriole. 2.Afferent arterioles have a larger diameter than the efferent arteriole, where blood leaves glomerulus, creating high blood pressure or high hydrostatic pressure 3.This forces water, urea, salts and other small solutes such as glucose, amino acids into the Bowman’s capsule, while blood cells and large molecules such as protein remain in the capillaries. 4.The glomerular filtrate passes from the Bowman’s capsule into the proximal convoluted tubule. •The endothelium of the glomerular capillaries and the basement membrane of the Bowman’s capsule that wraps around the glomerular capillaries are partially permeable —> only small soluble substances are able to pass through.

urine formation selective reabsorption Cortex Medulla Selective reabsorption 1.At proximal convoluted tube, most of the mineral salts and all of the glucose and amino acids are absorbed through active transport or diffusion. Water is reabsorbed by osmosis. 2.Reabsorption of water continues in the loop of Henlé. 3.Water and salts are reabsorbed in the distal convoluted tubule. 4.Water is reabsorbed from the collecting duct (not part of nephron). 5.Excess salts, nitrogenous waste products, excess water enter the renal pelvis as urine and are excreted out of the body