Excretion Flashcards
What is excretion?
Process by which toxic waste products of metabolism/substances in excess of requirement are removed from the body
Example of excretion?
Lungs excrete CO2 (waste product) by gas exhale /exhalation
Kidneys produce urine that contains waste product, urea, in solution
Metabolic waste example and how are thye produced?
CO2- from DECARBOXYLATION of respiratory substrates
Nitrogenous waste - ammonia,urea,uric acid
- ammonia from deamination of excess amino acids
Bile pigments - from breakdown of haemoglobin
Urea - ornithine cycle in liver cells
Uric acid - break down of adenine/guanine (purines) in liver
LIVER PRODUCES ALL THESE EXCRETORY SUBSTANCES EXCEPT CO2
Why is excretion important?
Key process in homeostasis
Important in maintaining metabolism - metabolic waste can have bad consequences if accumilates
Effect on body if metabolic waste products accumulate?
CO2 - cell damage if blood pH falls below normal range (acidosis)
Ammonia- increase cytoplasm pH/interfere with metabolic processes (respiration) /receptors for neurotransmitters in brain
Urea - diffuses into cells DECREASING THEIR WP- can burst
URIC ACID: form crystals in joints- cause GOUT (painful form of arthritis)
BILE PIGEMNTS: turn skin yellow - jaundice
Liver external structure?
Good blood supply :
HEPATIC ARTERY - carry OX BLOOD from heart—> liver
(oxygen used for aerobic respiration, fuel metabolic activity in liver cells)
HEPATIC PORTAL VEIN - blood from digestive system —> liver via this vein
(allows liver to absorb/metabolise nutrients absorbed into blood in SI)
HEPATIC VEIN - deoxygenated blood exits liver via this vein /flow back to HEART
What is the liver connected to and what is its role?
Gall bladder
Role:
Store bile - bile contains bile salts for lipid digestion/bile pigments
Release bile - into duodenum via bile duct
Internal liver structure?
Liver consist of cells = HEPATOCYTES
Liver cells arranged into LOBULES - each one is supplied with blood by BRANCHES OF HEPATIC ARTERY/HEPATIC PORTAL VEIN
- blood from hepatic artery/portal vein MIXES in each lobule in wide capillaries (SINUSOIDS)
- each lobule connected to branch of HEPATIC VEIN that drains blood away/into main hepatic vein
What is the role of sinusoids?
Blood flowing through sinusoids can exchange substances with nearby hepatocytes
- allows hepatocytes to performs all functions of liver
liver fucntions?
Storage of glycogen
Formation of urea
Detoxification
How does the liver store glycogen?
- Plays a role in GLYCOGENESIS : convert glucose —> glycogen
- glycogen produced from GLYCOGENOLYSIS is stored IN HEPATOCYTES
How does the liver form UREA?
Amino acids in blood transported to liver via hepatic portal vein
Excess amino acids processed in hepatocytes during 2 step process involving :
- deamination
- ornithine cycle
What happens in deamination?
Amino group (NH2) removed from each amino acid , with an extra H+ atom
NH2 + H+ —> NH3 (ammonia)
Part of amino acid remaining after deamination = KETO ACID which can:
Enter Krebs cycle to be respired
Be converted to glucose
Be converted to glycogen/fat for storage
What happens in ORNITHINE CYCLE?
Ornithine cycle - Series of events where ammonia is converted to urea
2NH3 + CO2 —> CO(NH2)2 + H2O
- form urea which diffuses through phospholipid bilayer of hepatocytes/transported to kidneys in blood plasma where its excreted
What is detoxification?
Detoxificaton - breakdown of substances that are not needed or are toxic
- alcohol, hydrogen peroxide,lactate, medicines
How is alcohol detoxified?
Alcohol absorbed in stomach/transported in blood to HEPATOCYTES
Enzyme ALCOHOL DEDHYDROGENASE in hepatocytes converts
ethanol —> ethanal —> other molecules that enter respiration
Why can continuous detoxification cause liver problems?
Metabolism of ethanol generates ATP
- so hepatocytes wont metabolise as much fat as usual/store the fat —> FATTY LIVER
- stored fat reduces ability of hepatocytes to carry out other functions/lead to cirrhosis - SCARRING OF LIVER
What are the two main functions of the kidneys?
- As an osmoregulatory organ, they regulate the water content of the blood vital for maintaining blood pressure.
- As an excretory organ, they excrete toxic waste products of metabolism (such as urea) and substances in excess of requirements (such as salts).
What does the renal artery/vein do?
Artery: Carries oxygenated blood (containing urea and salts) to the kidneys
Veins :Carries deoxygenated blood (that has had urea and excess salts removed) away from the kidneys.
What is the role of the ureter?
Carries urine from the kidneys to the bladder.
What surrounds the kidney?
tough outer layer - the fibrous capsule.
What are the three main areas of the kidney?
- Cortex (contains glomerulus, Bowman’s capsule, proximal convoluted tubule, and distal convoluted tubule of the nephrons).
- Medulla (contains the loop of Henle and collecting duct of the nephrons).
- Renal pelvis (where the ureter joins the kidney).