Body Structure and Function

BODY STRUCTURE AND FUNCTION

Chapter 9

A STEADY STATE

• Homeostasis is crucial for health and survival.
• Various body functions and processes work together to promote homeostasis.
• Homeostasis can be compromised by illness, disease, and injury.

ORGANIZATION OF THE BODY

• The basic unit of body structure is the cell.
• Groups of cells with similar functions combine to form tissues.
• Groups of tissues performing the same function develop into organs.
• An aggregation of organs that work together to perform specific functions results in systems.

THE INTEGUMENTARY SYSTEM

• The integumentary system, commonly known as the skin, is the largest system of the body.
• It consists of two primary layers:
  • Epidermis: the outer layer.
  • Dermis: the inner layer, below the epidermis.
• Additionally, the skin is associated with subcutaneous tissue (fat).

FUNCTIONS OF THE SKIN

• Acts as the body's protective covering against external elements.
• Prevents microorganisms from entering the body.
• Prevents excess amounts of water from escaping the body.
• Protects internal organs from physical injury.
• Contains nerve endings that can sense pleasant or unpleasant stimulation.
• Aids in regulating body temperature.
• Serves as a reservoir for fats and water.

THE MUSCULOSKELETAL SYSTEM

• The musculoskeletal system provides structural support for the body.
• Enables body movement and locomotion.
• Protects internal organs and contributes to the overall shape of the body.

BONES

• The human body contains 206 bones.
• There are four main types of bones:
  • Long bones: Responsible for bearing the body's weight.
  • Short bones: Facilitate skillful and easy movements.
  • Flat bones: Protect internal organs.
  • Irregular bones: Allow for various degrees of movement and flexibility.
• Bone marrow within bones produces blood cells.

JOINTS

• A joint is a connection point between two or more bones, allowing for movement.
• There are three major types of joints:
  • Ball-and-socket joints: Allow movement in multiple directions (e.g., shoulder and hip).
  • Hinge joints: Permit movement in one direction (e.g., elbow).
  • Pivot joints: Allow rotational movement (e.g., skull connection to the spine).

MUSCLE TYPES

• Muscles can be categorized based on control:
  • Voluntary muscles: Muscles that can be consciously controlled.
  • Involuntary muscles: Muscles that function automatically.
  • Cardiac muscle is a type of involuntary muscle.
• The three primary functions of muscles include:
  • Movement of body parts.
  • Maintenance of posture or muscle tone.
  • Generation of body heat.

THE NERVOUS SYSTEM

• The nervous system is responsible for controlling, directing, and coordinating all body functions.
• It consists of two main divisions:
  • Central nervous system (CNS): Comprises the brain and spinal cord.
  • Peripheral nervous system: Includes the nerves spread throughout the body.

CENTRAL NERVOUS SYSTEM

• The brain is protected by the skull and consists of three major parts:
  • Cerebrum
  • Cerebellum
  • Brainstem

PERIPHERAL NERVOUS SYSTEM

• The peripheral nervous system includes 12 pairs of cranial nerves and 31 pairs of spinal nerves that connect the CNS to the rest of the body.

SENSE ORGANS

• The five senses include:
  • Sight: Vision; processed by eyes which have three layers:
  • Sclera: Outer layer.
  • Choroid: Middle layer.
  • Retina: Inner layer.
  • Hearing: Processed by the ear which consists of three parts:
  • External ear
  • Middle ear
  • Inner ear

THE CIRCULATORY SYSTEM

• The circulatory system consists of the blood, heart, and blood vessels.
• It has multiple functions including:
  • Transporting nutrients, hormones, and other substances to cells.
  • Facilitating gas exchange (oxygen and carbon dioxide).
  • Eliminating waste products from cells.
  • Helping maintain the body's fluid balance.
  • Assisting in body temperature regulation.
  • Producing and transporting cells that defend the body against diseases.

BLOOD COMPONENTS

• Blood is made up of blood cells and plasma;
  • Plasma: Primarily consists of water.
  • Red blood cells (RBCs), or erythrocytes: Responsible for the red color due to hemoglobin.
  • White blood cells (WBCs), or leukocytes: Defend against infections.
  • Platelets (thrombocytes): Crucial for blood clotting.

THE HEART

• The heart is a muscular organ that pumps blood throughout the body.
• Structure of the heart includes three layers:
  • Pericardium: Outer layer.
  • Myocardium: Thick muscular layer.
  • Endocardium: Inner lining of the heart.
• The heart is comprised of four chambers:
  • Atria: Upper chambers that receive blood.
  • Ventricles: Lower chambers that pump blood (the left ventricle pumps blood to the entire body).

BLOOD VESSELS

• Arteries: Carry blood away from the heart; the largest artery is the aorta.
• Arterioles: The smallest branches of arteries.
• Capillaries: Tiny vessels that facilitate exchange between blood and tissues, removing waste products.
• Veins: Return blood to the heart; the major veins are the inferior vena cava and superior vena cava.

THE LYMPHATIC SYSTEM

• The lymphatic system is a complex network responsible for transporting lymph.
• Functions include:
  • Collecting excess lymph from tissues and returning it to the blood, aiding fluid balance.
  • Defending against infections by producing lymphocytes.
  • Absorbing fats from the intestines and transporting them to the bloodstream.

STRUCTURES OF THE LYMPHATIC SYSTEM

• Right lymphatic duct: Collects lymph from the right arm and right side of the head, neck, and chest, empties into a vein on the right side of the neck.
• Thoracic duct: Collects lymph from the pelvis, abdomen, lower chest, and the rest of the body, emptying into a vein on the left side of the neck.
• Tonsils and adenoids: Trap microorganisms in the mouth and nose to prevent infection.
• Spleen: The largest component of the lymphatic system; filters bacteria, destroys old RBCs, and stores blood.

THE RESPIRATORY SYSTEM

• The respiratory system is tasked with bringing oxygen into the lungs and removing carbon dioxide from the body.
• Respiration involves two phases:
  • Inhalation (inspiration): Intake of oxygen.
  • Exhalation (expiration): Release of carbon dioxide.
• This system supplies oxygen necessary for cellular function.

STRUCTURE OF THE LUNGS

• The lungs are composed of spongy tissue filled with alveoli, blood vessels, and nerves.
• Each lung has distinct lobes and is protected by the diaphragm, which separates it from the abdominal cavity.
• Each lung is encased in a two-layered sac called the pleura.
• Bony frameworks consisting of ribs, sternum, and vertebrae offer protection for the lungs.

THE DIGESTIVE SYSTEM

• Also referred to as the gastrointestinal (GI) system.
• Major functions include:
  • Physically and chemically breaking down food for nutrient absorption.
  • Removing solid waste from the body.
• Peristalsis is the involuntary muscular movement that propels contents through the digestive system.

COMPONENTS OF THE DIGESTIVE SYSTEM

• Involves the entire GI tract and accessory organs.
• Major parts:
  • Mouth, pharynx, esophagus, stomach, small intestine, large intestine.
• Accessory organs include: teeth, tongue, salivary glands, liver, gallbladder, and pancreas.
• Digestion begins in the mouth; the gallbladder stores bile, a greenish liquid essential for fat digestion.

THE URINARY SYSTEM

• The urinary system's roles include:
  • Removing waste products from the blood.
  • Maintaining water, electrolyte, and acid-base balance in the body.

STRUCTURE OF THE URINARY SYSTEM

• Kidneys: Bean-shaped organs in the upper abdomen that filter blood and remove waste.
  • Each kidney contains approximately one million nephrons, the functional unit of the kidney.
• Ureters: Tubes that carry urine from kidneys to the bladder.
• Bladder: Stores urine; approximately 250 ml of urine is required to stimulate the urge to urinate.
• Urine exits the body through the urethra and the meatus.

THE REPRODUCTIVE SYSTEM

• Human reproduction involves the fusion of a male and a female sex cell.
• Structural differences between the male and female reproductive systems facilitate this process.

MALE REPRODUCTIVE SYSTEM

• The testes are the male sex glands (or gonads) that produce male sex cells (sperm).
• Testes are located in a sac called the scrotum.
• Sperm travel from the testes to the epididymis (coiled tube), then through the vas deferens, which joins the two seminal vesicles that store sperm and produce semen, the fluid that carries sperm to the reproductive tract.

FEMALE REPRODUCTIVE SYSTEM

• The ovaries are the female gonads that produce female sex cells (ova or eggs).
• The release of an ovum is known as ovulation.
• Ova travel through fallopian tubes to the uterus, where fertilization by male sperm can occur, leading to fetal development.

THE IMMUNE SYSTEM

• The immune system's primary function is to protect the body from disease and infections.
• It detects and responds to threats both within and outside the body.
• Upon sensing an antigen (an unwanted substance), the immune system activates a response.

COMPONENTS OF THE IMMUNE SYSTEM

• Involves various cells and substances that work together to produce immunity, including:
  • Antibodies: Proteins that recognize and neutralize pathogens.
  • Antigens: Substances that provoke an immune response.
  • Phagocytes: Cells that engulf and digest pathogens.
  • Lymphocytes: T cells and B cells that are crucial for adaptive immunity.
  • B lymphocytes (B cells): Responsible for producing antibodies.
  • T lymphocytes (T cells): Manage immune responses and destroy infected host cells.

STRUCTURAL COMPONENTS

• Essential structures related to the immune system include:
  • Mucous membranes: Line body cavities and produce mucus to trap pathogens.
  • Tonsils: Guard against pathogens entering the body through the mouth and nose.
  • Lymphatic vessels: Carry lymph that contains immune cells throughout the body.
  • Thymus: Site of T cell maturation.
  • Spleen: Filters blood and lymph, removing pathogens, and stores immune cells.
  • Bone marrow: Produces blood cells, including leukocytes.

THE ENDOCRINE SYSTEM

• The endocrine system comprises glands that secrete hormones into the bloodstream.
• Hormones regulate the activities of other organs and glands throughout the body.

MAIN ENDOCRINE GLANDS AND THEIR FUNCTIONS

• Pituitary gland: Known as the master gland, located at the base of the brain behind the eyes.

  • Anterior pituitary lobe functions:
  • Secretes growth hormone (GH) and hormones regulating reproductive system functions.
  • Posterior pituitary lobe functions:
  • Secretes antidiuretic hormone (ADH) and oxytocin.

• Thyroid gland: Located in the neck in front of the larynx, secretes thyroid hormone (TH) or thyroxine.

• Parathyroid glands: Consist of four glands located adjacent to the thyroid, secrete parathormone.

• Adrenal glands: Two glands that secrete epinephrine and norepinephrine along with hormones essential for life:

  • Glucocorticoids: Involved in metabolism and stress response.
  • Mineralocorticoids: Regulate electrolyte and water balance.
  • Small amounts of male and female sex hormones.

• Thymus: Produces thymosin, crucial for T cell development.

• Pancreas: Secretes insulin, essential for glucose metabolism.

SUMMARY

• Each system discussed plays a significant role in maintaining homeostasis and overall health, highlighting the interconnectedness of body functions and the significance of physiological balance.