Human Physiology: Chapter 1

What is Physiology?

Study of biological function; how the body works

a. Concerned with the normal function of cells to the organism as a whole

b. Emphasizes mechanisms – how it works

c. Explains using cause and effect sequences

d. Derived from scientific experiments

pathophysiology

a. Concerns how disease or injury affects physiological processes

b. Aids understanding of normal processes

comparative physiology

a. Studies the differences and similarities in the functions of invertebrates and vertebrates

b. Has aided in the development of pharmaceutical drugs

brief history of physiology

• Aristotle – Greece (384 to 322 BC) – speculated about body function (thinkers, not doers)

• William Harvey – England (1578 to 1657) – demonstrated that the heart pumps through a

closed system of vessels

• Claude Bernard – France (1813 to 1878) – observed that the internal environment (milieu

intérieur) stays relatively constant although changes are occurring

• Walter Cannon – U.S. (1932) – coined the term homeostasis to describe the internal

consistency of the body

homeostasis

constancy of the internal environment.

The main purpose of our physiological mechanisms is to maintain homeostasis.

Deviation from homeostasis indicates disease.

Homeostasis is accomplished most often by negative feedback loops.

Pathway of negative feedback loops

a. Receptors, which act as sensors in the body to detect change and send information to the:

b. Integrating center, which assesses change around a set point. The integrating center then sends instructions to an:

c. Effector (muscles or glands), which can make the appropriate adjustments to counter the change from the set-point

Mechanism of negative feedback loops

a. Moves in the opposite direction from the change

b. Makes the change from the set-point smaller

c. Reverses the change in the set-point

d. This is a continuous process, always making fine adjustments to stay in homeostasis

Body Temperature Example of Negative Feedback Loops

a. Sensors in the brain detect deviation from 37°C. Another part of the brain assesses this as actionable, and effectors (sweat glands) are stimulated to cool the body.

b. Once the body is cool, sensors alert the integrating center, and sweat glands are inhibited.

c. The end result regulates the entire process. Production of the end product shuts off or down-regulates the process. Therefore it is called a negative feedback loop.

Antagonistic Effectors

a. Homeostasis is often maintained by opposing effectors that move conditions in opposite

directions.

This maintains conditions within a certain normal range, or dynamic constancy.

When you are hot, you sweat; when you are cold, you shiver. These are antagonistic

reactions.

b. Other examples – blood glucose levels, blood calcium levels, heart rate, and blood pH

Quantitative Measurements

a. In order to study physiological mechanisms, scientists must measure specific values and mathematically determine such statistics as their normal range, their averages, and their deviations from the average (which can represent the set point).

b. A knowledge of normal ranges aids in diagnosing diseases and in assessing the effects of drugs and other treatments in experiments.

positive feedback

The end product in a process stimulates the process.

The action amplifies the changes that stimulated the effectors

Positive feedback could not work alone, but it does contribute to many negative feedback loops.

a. For example, if a blood vessel is damaged, a process is begun to form a clot. Once the damage is fixed, clotting ends (negative feedback). However, the process of forming the clot involves positive feedback.

b. The strength of uterine contractions during childbirth is also regulated by a positive feedback loop.

intrinsic regulation

Cells within the organ sense a change and signal to neighboring cells to respond appropriately.

extrinsic regulation

The brain (or other organs) regulates an organ using the endocrine or nervous system.

The endocrine system releases hormones into the blood, which transports them to the target organ(s).

The nervous system “innervates” organs with nerve fibers.

feedback control of hormone secretions

Hormones are secreted in response to specific stimuli.

a. Example - An increase in blood sugar results in the release of insulin, which removes sugar from the blood.

Secretion can be inhibited by its own effects.

a. Example - Decreased blood sugar inhibits the release of insulin.

Negative feedback inhibition (a closed-loop control system) usually involves an antagonist to make sure homeostasis is maintained within normal levels.

a. Example - When blood sugar is low, the hormone glucagon is secreted, which results in a rise in blood sugar.

negative feedback inhibition

(a closed-loop control system) usually involves an antagonist to make sure homeostasis is maintained within normal levels.

a. Example - When blood sugar is low, the hormone glucagon is secreted, which results in a rise in blood sugar.

levels of organization

Cell – basic unit of structure and function of living things

Tissue – group of similar cells that perform a similar function

Organ – group of two or more tissues into structural and functional units

System – group of organs that work together to perform related functions

Organism – systems working together in coordination

primary tissues

Our organs are composed of four major categories of tissues:

a. Muscle tissue

b. Nervous tissue

c. Epithelial tissue

d. Connective tissue

Each tissue has structures and functions that dictate the physiology of the organ.

muscle tissue

Specialized for contraction

The three types are:

a. Skeletal muscle

b. Cardiac muscle

c. Smooth muscle

skeletal muscle tissue

a. Voluntary muscle (muscle you can consciously control)

b. Most associated with bones that are pulled to produce movements

c. A few do not cause skeletal movement but are under conscious control - tongue,

esophagus, sphincters, and diaphragm

d. Has visible striations from sarcomeres

e. Union of separate cells called myoblasts to form myofibers – a syncytium

f. Can produce a graded response

cardiac muscle tissue

a. Found only in the heart

b. Fibers are short, branched, and interconnected both physically and electrically

c. Striated, but very different in structure and action from skeletal muscle.

d. Involuntary (you can not consciously control)

e. Specialized cell connections called intercalated discs allow passage of sodium ions between cells.

f. Cannot produce a graded contraction

smooth muscle tissue

a. Found in the walls of digestive, urinary, and reproductive organs, blood vessels, and bronchioles of the lungs (hollow organs)

b. Not striated, involuntary

c. Generally found in layers that run different directions

d. Peristalsis – coordinated, wave-like contraction of smooth muscle layers to more substances through the organs

Peristalsis

coordinated, wave-like contraction of smooth muscle layers to more substances through the organs

nerve tissue

Found in the brain, spinal cord, and nerves

Composed of neurons and neuroglia

Neurons conduct impulses and have three parts:

a. Dendrites: short, highly branched, cytoplasmic extensions that receive signals

b. Axon: long, single extension that sends signal

c. Cell body: metabolic center containing the nucleus

Neuroglia are supporting cells that do not conduct a nerve impulse but are essential for neuron function

epithelial tissue

Forms the membranes that cover body surfaces and line the inside of hollow organs, and glands

Epithelial membranes are classified by the number of layers:

a. Simple epithelium has one layer and is specialized for transport of substances.

b. Stratified epithelium is composed of multiple layers and provides protection

simple epithelium

has one layer and is specialized for transport of substances

stratified epithelium

composed of multiple layers and provides protection

how is epithelial tissue classified by shape

a. Squamous: flattened cells

b. Cuboidal: as tall as they are long

c. Columnar: tall cells

Put the cell shape together with the number of layers to name epithelial tissue

Some modifications can occur such as in columnar tissues that have goblet cells that secrete mucus and cilia that move in a coordinated fashion

simple epithelial tissues

a. Simple squamous epithelium allows for rapid diffusion as in the alveoli of the lungs

b. Simple cuboidal epithelium allows for secretion of substances as in various glands

c. Simple columnar epithelium allows for absorption as found in the wall of the small intestine

stratified epithelial tissue

a. To provide protection, cells of stratified epithelial tissues are held together by structures called intercellular junctions (collectively known as junctional complexes).

These are too close together to house blood vessels, so are nourished by connective tissues beneath.

Epithelial tissues are attached to connective tissues by a basement membrane.

a. Nonkeratinized membranes have living cells in all layers

b. Keratinized membranes have cells filled with keratin, a water-resistant protein, and layers of dead cells on the surface

exocrine glands

a. Derived from epithelial tissues

b. Secretions are transported by ducts.

Examples include lacrimal, sweat, and sebaceous glands; digestive enzyme glands; and the prostate.

c. Secretory portions may be tubes or acini groups

d. Sweat glands

Eccrine or merocrine - more numerous; secrete a salty sweat; involved in thermoregulation

Apocrine – located in axilla and pubic region; protein-rich sweat that bacteria feed on

endocrine glands

a. These are derived from epithelial tissues.

b. Endocrine glands lack ducts and therefore secrete into capillaries within the body.

c. The structure of endocrine glands will be described in chapter 11.

e. Examples include many hormone producing glands such as the thyroid gland, adrenal glands, etc.

connective tissue

Characterized by a matrix made up of protein fibers, extracellular material, and specialized cells

There are four major categories:

a. Connective tissue proper

b. Cartilage

c. Bone

d. Blood

connective tissue proper

a. Composed of protein fibers and a gel-like ground substance

b. Subtypes:

Loose: collagen fibers scattered loosely with room for blood vessels and nerves

Example: dermis of the skin

Dense regular: Densely packed collagen fibers with little room for ground substance

Examples: tendons and ligaments

loose connective tissue

collagen fibers scattered loosely with room for blood vessels and nerves

Example: dermis of the skin

dense regular connective tissue

Densely packed collagen fibers with little room for ground substance

composed of densely packed collagen fibers in

various arrangements to resist forces

Examples: tendons and ligaments

cartilage connective tissue

a. Composed of cells called chondrocytes surrounded by a semi-solid ground substance

b. Serves as a template skeleton during bone development

c. Found in joints to provide a gliding surface for bones

bone connective tissue

a. Cells called osteoblasts trap mineral salts, forming concentric layers of calcified material around a canal filled with blood vessels and nerves.

b. Once the matrix has hardened, the cells are called osteocytes and live-in spaces called lacunae.

c. The dentin of a tooth is similar to bone and is made by cells in the pulp; the outer enamel is harder than bone or dentin.

organs

An organ is composed of two or more tissues that serve different functions in the organ.

The skin is the largest organ in the body.

a. The skin has all four primary tissues.

b. Epidermis – keratinized stratified squamous epithelium to protect against water loss and abrasion

c. Dermis – dense irregular connective tissue containing exocrine glands, hair follicles, sense receptors, and blood vessels

d. Hypodermis – adipose tissue for padding and insulation

organ systems

Organs that perform related functions are grouped into systems.

Humans have 11 inter-related organ systems

body fluid compartments

Intracellular: area inside the cells; contains 65% of total body water

Extracellular: area outside the cells; examples: blood plasma and interstitial fluid

Both body fluid compartments are filled primarily with water and are separated by membranes.

There is selective movement of molecules and ions between the compartments through the cell membrane.