Human Physiology:Human Physiology:How Does the

Human Body Work?

How Does the

Human Body Work?

Homeostatic Control System

How Do Parts of The body Communicate?

• How does the body quickly send information to anatomical structures?

• Diffusion of substances is effective for short distances.

• However, moving information quickly over long distances is the function of the nervous system.

The Nervous System Provides Rapid Communication

• Organization of the nervous system– Central nervous

system: brain and spinal cord

– Peripheral nervous system: nerves

The Nervous System Provides Rapid Communication

• Functions of the nervous system:– Thought, language, learning and

comprehension. • Occurs at the brain

– Reflexes• Controlled by spinal cord

The Nervous System Provides Rapid Communication

• Two types of neurons:– Sensory: receives

information about the outside world or about conditions in the body and sends it to the brain.

– Motor: brain sends messages through these neurons to tissues and organs to that affect a response

The Nervous System Provides Rapid Communication

• Neurons conduct electrical impulses– To increase the speed

of conductance, axons are insulated by myelin sheaths produced by Schwann cells.

Action Potentials

• Form of electrical impulses.

• Transient all-or-none reversals in electrical potential across a neuronal membrane that rapidly move from dendrites, to cell body, to axon.

Action Potentials

• Disruption of ion balance outside or inside the cell causes membrane potential to reach threshold which causes opening of sodium gated ion channels.– Allows sodium ions to enter cell and cause inside of the

cell to have + charge.

• This causes opening of potassium gated channels which allows potassium to exit the cell.– Returning the negative charge to the inside of the cell.

Synapses• Junction between one neuron and another neuron

or muscle or gland.• When the action potential travels to the end of the

neuron, it stimulates the release of neurotransmitter (such as acetylcholine) into the synapse.

• The neurotransmitter travels across the synapse and binds to protein receptors on the membrane of another cell.– Can initiate another action potential.

Functional Divisions of the Nervous System

• Two divisions:– Somatic:

• responsible for our voluntary actions

– Autonomic: • works to maintain our body’s homeostasis

independently of our conscious will.• Two Types

– Sympathetic– Parasympathetic

Endocrine System

• Second system for communication– Works by means of hormones (chemicals) which

travel in the bloodstream to a distant group of target cells where they render their effect.

• Coordinates slower, more long-term responses such as growth, maturation, reproduction and water balance.

Endocrine System

• Target cells have specific receptors that bind and recognize only that hormone.

• When a hormone binds, the target cell responds in one of three basic ways:– Change some aspect of the cells metabolism– Influence the movement of substances across the

cell membrane.– Turn gene expression on or off

• Altering protein synthesis

Hypothalamus and Pituitary Glands• Found in the brain

– Control many vital functions of the body.

• Hypothalamus:– Regulates temperature, water balance,

appetite, thirst, growth, waking, sleeping, and reproduction.

• Pituitary has two divisions:– Anterior and Posterior.

Posterior Pituitary

• Releases two hormone that are made in hypothalamus and stored in posterior pituitary gland– Antidiuretic hormone (ADH)

• Causes body to conserve water and release less in the urine.

– Oxytocin• Induces contractions in the uterus needed for childbirth• Induces the release of milk from the breast.

Anterior Pituitary

• Hypothalamus produces releasing hormones and release-inhibiting hormones. – These hormone are released into the blood

and travel a short distance to the anterior pituitary gland

– Regulate the activities of the pituitary gland

Negative Feedback

• Serves as a mechanism for regulating the release of hormones in the endocrine system.

• Without negative feedback, a response designed to bring some aspect of the body back to homeostasis could easily overcompensate.– Pushing it in the opposite direction.

How Do Humans Acquire and Process Nutrients and Get Rid of Wastes?

• If we were simple-celled organisms we could acquire the nutrients we need through diffusion across our membrane.

• Digestive, respiratory, circulatory, urinary systems help us obtain the nutrients we need as multicellular organisms.

Digestive Tract

• It is a long hollow tube that begins at the mouth and ends at the anus.

• Function:– Take in food, store it and prepare it to enter

the cells of the body.• Need to digest proteins, carbohydrates and lipids

in order to for cells to use them as raw materials and energy.

Processes involved in breaking down and taking in food:

• Digestion: breaking down food into smaller molecules using digestive enzymes.

• Secretion: release of digestive enzymes, acids, and other substances that aid in digestion.

• Motility: movement of food and digestive secretions through the digestive tract.

• Absorption: entry of simple molecules produced by digestion across the digestive tract wall into the blood and finally to the cells of the body.

Mouth and Esophagus

• Mouth:– Beginning of the digestive tract– Chewing occurs here– Digestive enzymes in saliva start begin digesting

carbohydrates

• Esophagus:– Tube that connects the mouth and the stomach

Stomach

• Functions:– Stores food for a brief

time and moves it into the intestines in small amounts after it is liquefied.

– Digestion of proteins.– Acid in the stomach

also protects the body against bacterial invasion.

Stomach• Peristalsis:

– Waves of muscular contractions that move the chyme into the small intestines

• Chyme: liquified food

• Movement of food out of the stomach is regulated by the pyloric valve

Intestines

• Are about 14 feet long with many twists and turns.– Inner wall surface area is over 100 feet.

• Important for increase absorption.

• Small intestines:– Digestion occurs in its final stages here.– Pancreatic enzymes help in digestion.

• Pancreas also release bicarbonate to neutralize the acid from the stomach.

Liver

• Releases bile– Stored in gallbladder.– Mixture of bile salts and bicarbonate

• Bile salts emulsify fat (break it down into smaller globules)

• Both pancreatic secretions and bile enter the small intestines through the bile duct.

Movement in the Small Intestines

• Segmentation– Responsible for the

majority of muscle movement in the small intestines.

– Moves the chyme.

Absorption in the Small Intestines

• Structure of the small intestines facilitates absorption of food into the cells of the small intestines.– Molecules then move into the blood and

finally to the cells.

Absorption in the Small Intestines

Large Intestines

• 5 feet of tubing

• All that remains of the chyme is– indigestible material, water, bacteria, and a

few other things that could not be absorbed.

• Primary role:– Store fecal material, absorb water from it and

propel it to the rectum.

Respiratory System

• Functions:– Exchange oxygen and carbon dioxide.– Regulate pH of the body.– Used for vocalization.– Protects the body form inhaled irritants or

pathogens.

Structure of Respiratory System

Ventilation

• Is the movement of air between the alveoli and the environment– When the diaphragm contracts, it allows air to

enter the lungs.• Oxygen moves by diffusion into the oxygen-poor

blood.

– When the diaphragm relaxes, the air leaves the lungs.

• Carbon dioxide diffuses from the blood into the air spaces of the lung and is expelled.

Cardiovascular System

Cardiovascular System

• Consists of :– Heart, arteries, capillaries, veins.

• Primary role of blood:– is to transport substances to and from all

parts of the body.• Moves nutrients, wastes, and chemical

messengers (hormones).

Heart

• Consists of four chambers:– 2 atria (atrium)– 2 ventricles

• Has four valves:– Bicuspid, Tricuspid – Pulmonary, Aortic

Heart

• Consist two pumps– Pulmonary Circulation:

• Blood travels from the heart to the lungs and back to the heart.

– Systemic Circulation:• Blood travels through arteries to capillaries to veins

and back to the heart.

Heartbeat

• Pacemaker cells– Found in the right atrium in the region of the

sinoatrial node.– Initiates electrical impulses.

• Passes to all the other cells in the heart.• Responsible for initiating contraction of the heart

muscle.

Urinary System

• Removes metabolic wastes.

• Consists of:– Kidneys and urinary

bladder.

• Functional unit is the nephron.– Over a million in each

kidney.

Nephron

• Cleanse the blood and use three processes to do so:– Filtration – Reabsorption– Secretion

Nephron

• A protein-free, cell-free filtrate of the blood enters the nephron tubule at one end.

• As the filtrate moves through the nephron tubule substances such as sodium chloride, water and glucose are removed.

• Other substances such as potassium ions, hydrogen ions and drugs are added to the filtrate from the blood.

Nephron

• Effect of hormones on urine production:

– ADH • Causes the body to retain water

–Preventing it from showing up in the urine

• Causes urine concentration to increase

How Does the Human Body Move?

• Muscles exert a force that causes movement

• Three types of muscle in the body:– Skeletal: attached to bones– Cardiac: heart muscle– Smooth: tissue that surrounds hollow organs

Skeleton Provides the Framework

• Cartilage – Primary component of

baby skeleton.– Persists in adults in

places where firmness and flexibility are needed.

Skeleton Provides the Framework

• Bone – Mostly made of a

calcium-rich matrix that exists outside of cells.

Skeleton Provides the Framework

• Ligaments – Are strong, flexible bands that connect

cartilages or bones together at points of attachment called joints.

• Tendons– Attach skeletal muscle to bones.– Are tough bands of white connective tissue.

Muscle Provides Movement

• Muscles cause movement by contracting

• Muscle tissue is organized at many different levels– Muscles are composed of fibers

• Each fiber is a single cell.

Muscle Provides Movement

Muscle Provides Movement

• Muscle fibers contain two proteins– Actin: thin protein– Myosin: thick protein

• When these two fibers slide past one another, muscle contraction occurs.

• Process is fueled by ATP.

Muscle Provides Movement

Role of the action potential in muscle contraction

• Action potentials are the stimulus that initiates muscle contraction.

• Action potentials cause muscle to release calcium from sarcoplasmic reticulum.– Calcium interacts with

actin to cause muscle contraction.

How Do Humans Reproduce?

• They reproduce sexually by a process that requires coordinated activities of the male and female reproductive systems

• Both systems produce gametes through the process of gametogenesis– Meiosis is a component of this process.– Occurs in woman’s ovaries and men’s testes.

How Do Humans Reproduce?

• Gametogenesis in both sexes is influenced by hormones released from the brain and the gonads.

Male Reproductive Tract

• LH and FSH– Released from the pituitary.– Stimulate gonads to produce gametes and

testosterone.• Testosterone is required for gametes to mature

– Also responsible for secondary sex characteristics in men.

Male Reproductive Tract

Female Reproductive Tract

• Gametogenesis occurs before birth.– Only one egg reaches maturity during monthly

cycle.

• Ovaries contain follicles.– Small sac-like structures holding one egg

(oocyte) surrounded by accessory cells.

• The menstrual cycle allows for maturation and release of the egg.

Female Reproductive Tract

Menstrual Cycle

• Cycle begins with menstruation.– Sloughing of the endometrium.

• Cycle is marked by a mid-month event.– Ovulation: Single egg is released from the

ovary.

• All of these events are regulated by changes in different levels of sex hormones.

Menstrual Cycle

Pregnancy

• Egg is fertilized by a sperm on its way to the uterus.– Forms a zygote

• Zygote begins dividing, becoming an embryo.

• Embryo may implant in the endometrium, resulting in pregnancy.

How Does the Body Fight Disease?

• Human body is challenged by pathogens.– Disease-causing microbes

• Bacteria and viruses are most common type

• The function of the immune system is to protect you from the disease causing organisms.– Immunity is a combination of generalized non-

specific defenses and highly specific defenses against particular invaders.

Immune system

• Tissues that affect the immune system response are scattered throughout the body– Main cells of the

immune system are leukocytes

• Produced in bone marrow and mature in thymus

Immune system

• First line of defense:– Shields that create barriers.

• Examples: skin, stomach, and mucous layers of respiratory and digestive tracts.

– These defense make it difficult for invaders to gain access to the internal compartments of the body.

Cells of the Immune System

Immune system

• Second line of defense:– Nonspecific inflammatory response that

occurs at the site of infection.• Phagocytic leukocytes

– engulf invaders – Attract more immune cells to the site.

• Chemical defenses include – the release of histamines– Release of other chemicals that kill the cells directly

Immune system

• Third line of defense:– Most powerful line of defense directed at pathogens

that have been encountered more than once.– First encounter:

• Lymphocytes that produce antibodies that recognize an invader antigen are stimulated to proliferate and produce more antibodies

• Some of the progeny become memory cells that remain in the lymphoid tissue,

– ready to make antibodies in the event that the same antigen is encountered in the future