Excretory System Quiz and Flashcards: Questions and Answers

Study Notes

Excretory System

The excretory system is a collection of organs responsible for disposing waste from the body and maintaining osmotic balance in blood and plasma.

Osmoregulation

Osmoregulation is the process by which organisms control the balance of water and solutes within their bodies to maintain internal stability despite changes in external environmental conditions.

Processes of Excretion

There are 4 major processes of excretion: filtration, reabsorption, secretion, and excretion.
Filtration: pressure-filtering of body fluids producing a filtrate (water, salts, sugar, amino acids, N-waste).
Reabsorption: reclaiming of valuable solutes (glucose, salts, amino acids) from the filtrate.
Secretion: addition of larger molecules like toxins and other excess solutes from the body fluids to the filtrate.
Excretion: the filtrate leaves the system.

Primary Excretory Organs

The primary excretory organs in fish are the kidney, gills, and skin.

Fish Kidney Structure

The kidney is composed of the renal cortex (outer layer), renal medulla (inner layer), and renal pelvis (central area).
Renal cortex: responsible for filtering the blood and removing waste products.
Renal medulla: responsible for regulating the balance of fluids and electrolytes in the body.
Renal pelvis: receives blood from the renal arteries and returns it to the renal veins.

Types of Kidneys in Fish

Anterior kidney (head kidney or pronephros): plays a role in excretion during early development but is later replaced by the mesonephros and metanephros.
Posterior kidney (excretory kidney or metanephros): the permanent kidneys in vertebrates, responsible for filtering blood, removing waste products, regulating electrolyte balance, and maintaining proper fluid levels.

Freshwater vs Saltwater Fish Kidney

Freshwater fish kidneys excrete excess water and retain electrolytes, while saltwater fish kidneys excrete excess electrolytes and retain water.

Gills in Excretion

Gills play a role in excretion through the process of diffusion, removing metabolic waste such as carbon dioxide and ammonia.
Gills also regulate the balance of ions and maintain proper pH levels in the fish's body.

Skin in Excretion

Fish excrete waste through their skin via sweat glands.
Sweat contains salt, excess oils, water, and other unnecessary substances, which are then excreted through small pores.
Sweating also helps regulate body temperature during evaporation.

Excretory Organs in Shellfish

Coelom: a body cavity that serves as the excretory organ in shellfish such as clams and oysters.
Waste products are eliminated through the coelom via the process of filtration.

Description

Learn about the excretory system, a collection of organs responsible for disposing waste from the body and maintaining the osmotic balance. Explore the concept of osmoregulation and how organisms regulate water and solute levels internally.