Homeostasis & Body Structure Overview

Homeostasis & Excretion

• Homeostasis is the maintenance of a stable internal environment
• Homeostasis is necessary for normal body functioning and to sustain life
• Homeostatic imbalance is a disturbance in homeostasis, resulting in disease
• The body's cells require a stable internal environment (interstitial fluid) for survival and proper function
• The composition and temperature of the interstitial fluid must remain much the same
• Homeostasis involves the optimal concentration of gases, nutrients, and ions in the internal environment
• The body regulates homeostasis through neural and hormonal control systems

Structural Levels of the Body

• Chemical level: Atoms combine to form molecules
• Cellular level: Molecules form organelles, which make up cells
• Tissue level: Similar cells form tissues
• Organ level: Different tissues combine to form organs
• Organ system level: Organs work together to form an organ system
• Organism level: Organ systems work together to form an organism

Organ System Overview

• Integumentary: Forms the external body covering; protects deeper tissues and regulates body temperature
• Skeletal: Protects and supports body organs; provides muscle attachments for movement; site of blood cell formation and mineral storage
• Muscular: Produces movement; maintains posture; produces heat
• Nervous: Fast-acting control system; responds to internal and external changes; activates muscles and glands
• Endocrine: Secretes regulatory hormones; controls growth, reproduction and metabolism
• Cardiovascular: Transports materials in the body via blood pumped by the heart (Oxygen, Carbon Dioxide, Nutrients, Wastes)
• Lymphatic: Returns fluids to blood vessels; cleanses the blood and involved in immunity
• Respiratory: Keeps blood supplied with oxygen and removes carbon dioxide
• Digestive: Breaks down food; allows for nutrient absorption into the blood; eliminates indigestible material
• Urinary: Eliminates nitrogenous wastes; maintains acid-base balance; regulates water and electrolytes
• Reproductive: Produces offspring

Feedback Mechanisms

• Negative feedback is a control mechanism that acts against a change to return to a set point
• Negative feedback is used extensively to regulate homeostasis
• Negative feedback mechanisms shut off or reduce the initiating stimulus
• The response to the stimulus is negative, meaning it is in the opposite direction to the stimulus
• Negative feedback mechanisms maintain homeostasis

Thermoregulation

• All mammals maintain a constant body temperature (37ºC)
• Vasodilation occurs when the body temperature rises, blood vessels dilate to allow heat to be lost from the skin via convection and radiation
• Vasoconstriction occurs when the body temperature falls, blood vessels constrict to reduce blood flow near the surface, which reduce heat loss
• Heat loss via sweating is regulated by thermoreceptors in the skin, which detect an increase in body temperature
• The hypothalamus signals to the sweat glands to initiate sweating
• Evaporation off the skin causes cooling down
• The hypothalamus also sends messages to the blood vessels in the skin causing them to dilate, this allows more blood flow to the skin, where heat can be lost
• Heat from the blood is lost to the skin, allowing blood to return to the core of the body, controlling internal organs
• Thermoreceptors monitor changes in temperature
• The hypothalamus is the coordinating center and turns on the cooling system
• Skin blood vessels dilate and sweat glands initiate sweating, cooling the body
• Heat stress causes the body temperature to decrease; the hypothalamus turn the cooling system off
• During cold stress thermoreceptors message the hypothalamus, sends signals to constrict blood vessels to conserve heat, smooth muscles contract (causing hair to stand on end), skeletal muscles contract (causing shivering) , metabolic rate increases to produce heat to restore normal body temperature

Glucose Homeostasis

• Cells need a precise level of glucose in the blood to function properly
• Glucose moves into cells for cellular respiration
• Excess glucose is stored as glycogen in the liver
• Glucose levels are regulated by the hormones insulin and glucagon that are produced by the pancreas
• Insulin helps reduce sugar levels to reduce blood sugar and allows extra glucose to be stored in glycogen
• Glucagon helps increase sugar levels, releasing glucose when blood sugar is too low
• Type 1 and Type 2 diabetes are characterized by abnormal glucose regulation

Water Conservation

• The control of water levels is carried out by the kidneys
• Kidneys excrete urea, a waste product formed when the liver breaks down proteins
• Urea contains nitrogen
• Urine is excreted via the ureter and stored in the bladder

Urinary/Excretory System Functions

• Excretion
• Blood volume and blood pressure control
• pH regulation
• Concentration of solutes

Components of the Urinary System

• 2 kidneys
• 2 ureters
• 1 urinary bladder
• 1 urethra

The Kidneys

• Kidneys filter blood of waste products and control the amount of water in the body
• Nephrons are the functional units of the kidney; there are over 1 million nephrons per kidney
• The filtration process takes place in the glomerulus and Bowman's capsule
• Reabsorption of useful materials (glucose, ions, water) into the blood occurs in parts of the nephron

Components of a Nephron

• Renal corpuscle (Bowman's capsule and glomerulus)
• Proximal tubule
• Loop of Henle
• Distal tubule
• Collecting duct

Urine Formation

• Ultrafiltration: Blood enters capillaries where a network of capillaries forms a small knot called glomerulus, filtering small particles (glucose, water and ions) into the kidney tubule.
• Reabsorption: The body needs glucose in the blood for cellular respiration, thus glucose is transported from the tubule back into the capillary
• Reabsorption of water and ions: Water and ions are reabsorbed depending on the body's needs
• Excretion: Everything that is left (waste products such as urea and excess water) in the kidney tubule goes to the collecting ducts, and this waste is call urine which is eliminated from the body via the ureter to the bladder

Antidiuretic Hormone (ADH) Regulation

• ADH is released when blood solute concentration increases or blood pressure decreases
• ADH causes kidneys to absorb more water, decreasing urine volume
• The result maintains blood volume and blood pressure

Explore the essential concepts of homeostasis and the structural levels of the body with this quiz. Understand how the body maintains a stable internal environment and the hierarchy from chemical to organism level. Test your knowledge on these fundamental biological principles.