Chapter 1-7: Overview of Body Systems and Tissues

Integumentary System

1. Overview and Tissue Types

The transcript opens with an overview: the body has 11 body systems, which are groups of organs and tissues that work together to perform essential functions for survival and health, and these systems interact with one another. A key point is that there are four main tissue types—connective, muscular, nervous, and epithelial—that appear across all body systems and contribute to their structure and function.

1.1 Body Systems Interaction

For example, the urinary (excrtory) system cannot filter blood or remove waste without a functioning cardiovascular system providing the necessary blood supply and nutrients.

2. Skin Structure and Layers

The word integumentum in Latin means covering or shielding, which ties to the skin’s protective role. The integumentary system comprises the skin and its appendages (hair, nails, sweat glands) and serves multiple roles beyond shielding the internal environment. Skin thickness varies from about 1.5\ \text{mils} to 4\ \text{mils} depending on location; eyelids are thinner (around 0.5\ \text{mil}), while soles and palms are thicker (about 1.5-4\ \text{mils}). The skin’s color differences arise mainly from the amount and distribution of melanin, not from the presence or absence of skin components.

2.1 Skin Layers

Two skin layers are highlighted: the epidermis (outer) and the dermis (beneath).

2.2 Epidermis

The epidermis is the outermost layer made up of epithelial tissue; it is thin overall but provides protective functions. The epidermis itself has no direct blood supply; nutrients rely on the dermis’ capillaries. As epidermal cells (keratinocytes) migrate outward from the basal layer, they lose their nutrients and die, forming the stratum corneum, a hard, protective layer consisting of 20-30 layers of dead keratinocytes rich in keratin.

2.3 Epidermal Life Cycle

A simplified epidermal life cycle: stem cells in the deepest part of the epidermis (the stratum basale) actively divide; one daughter cell remains as a basal cell, while the other migrates toward the surface, changing characteristics as it ascends through layers until it reaches the stratum corneum and sloughs off. Everyday shedding of skin cells is substantial: about 8\ \text{g/day} and roughly 3\ \text{kg/year}. Dandruff can reflect accelerated turnover where skin cells mature and shed in 2–7 days instead of ~1 month.

2.4 Dermis

The dermis is deeper and is rich in connective tissue with a dense, irregular arrangement of collagen and elastic fibers, giving strength and elasticity. The dermis houses blood vessels that supply nutrients to deeper epidermal layers (like the stratum basale) and remove wastes.

3. Epidermal Cells

Key cells in the epidermis include keratinocytes (primary cells producing keratin) that are tightly bound, limiting substance passage. Keratinocytes also participate in vitamin D production when exposed to sunlight.

3.1 Keratinocytes

Keratinocytes (primary cells producing keratin) are tightly bound, limiting substance passage. Keratinocytes also participate in vitamin D production when exposed to sunlight.

3.2 Immune and Tactile Cells

Other epidermal cells include Langerhans (dendritic) cells that digest foreign substances and activate the immune system; Merkel (tactile) cells associated with sensory nerve endings for touch.

3.3 Melanocytes

Melanocytes produce melanin. Melanin is retained in keratinocytes and forms a protective shield over the nucleus against ultraviolet light. Although all humans have similar numbers of melanocytes, skin color differences reflect melanin type and amount.

4. Skin Appendages

Appendages of the skin include:

4.1 Hair

• Hair: formed by keratin; does not flake like the epidermis and serves protective roles (e.g., head hair for protection and heat retention; nasal hair filters incoming air).

4.2 Nails

• Nails: made of hard keratin, protecting fingertips and toes and aiding in object manipulation.

4.3 Sweat Glands

• Sweat glands: formed by myoepithelial cells (epithelial in origin) that contract to eject sweat; stimulated by the sympathetic nervous system.

4.4 Sebaceous Glands

• Sebaceous glands: secrete sebum, an oily substance that lubricates hair/skin and contains bactericidal components to reduce infection.

5. Hypodermis

Deep to the dermis lies the hypodermis (subcutaneous layer), consisting mostly of loose adipose tissue that attaches the skin to underlying fascia, allows skin movement without tearing, stores fat, insulates, and provides shock absorption.

6. Functions of the Skin

Functions of the skin include:

6.1 Physical and Chemical Protection

• Physical protection via keratinocytes and melanin-based UV protection.

• Chemical protection (lowering surface pH and bactericidal components in sebum).

6.2 Biological Defense

• Biological defense through dendritic cells and immune components.

6.3 Temperature Control and Sensation

• Temperature control via blood flow and sweating.

• Sensation through diverse sensory receptors for touch, pressure, nociception, and temperature.

6.4 Vitamin D Synthesis

• Vitamin D synthesis mediated by keratinocytes.

Skeletal System

1. Components and Functions

The skeletal system comprises bones, cartilage, ligaments, and their associated structures. It provides a frame for the body, supports soft organs, anchors skeletal muscles for movement, and protects soft tissues (e.g., the skull protecting the brain).

1.1 Mineral Storage and Hematopoiesis

Bones also store minerals such as calcium and phosphate, release them when needed, and participate in hematopoiesis within red bone marrow (primarily in proximal/distal ends of long bones) and fat storage in yellow marrow (occurs in the shaft).

1.2 Hormonal Role

The hormone osteocalcin, produced by bone, helps with glucose homeostasis.

2. Cartilage Types

Cartilage is an important connective tissue within the skeletal system and comes in three main types:

2.1 Hyaline Cartilage

• Hyaline cartilage (the most abundant; its name means glassy) provides flexibility and resilience, covers articular surfaces to reduce friction (articular cartilage) and is found in joints, costal joints, and growth plates. Because X-rays do not show cartilage, growth plates appear as gaps between bone shafts on X-ray images.

2.2 Elastic Cartilage

• Elastic cartilage contains more elastic fibers and is highly flexible; it is found in the ear and the epiglottis.

2.3 Fibrocartilage

• Fibrocartilage is highly compressible with great tensile strength, found in weight-bearing or tension-heavy sites such as the knee’s menisci and intervertebral discs. This type helps resist compression and shear.

3. Ligaments and Supportive Structures

3.1 Ligaments

Ligaments are dense regular connective tissue that connect bones across joints to stabilize them.

3.2 Bone Structure and Growth Plates

The skeletal system’s major components also include other supportive features like bones forming a rigid framework and the joints that allow movement. The role of cartilage and bone in structure-meets-function is evident: osteocytes and chondrocytes maintain the tissues, while the hard matrix of bone provides strong protective and supportive properties. The growth plates (epiphyseal plates) are regions of cartilage allowing growth in length during development.

Muscular System

1. Muscle Tissue Types

Muscle tissue drives movement and is highly vascularized to supply nutrients and remove wastes. The muscular system includes three main muscle types, each with distinct control patterns and functions:

1.1 Skeletal Muscle

• Skeletal muscle: voluntary control, attaches to bones, and pulls on the skeleton to produce movement.

1.2 Cardiac Muscle

• Cardiac muscle: involuntary, forms the heart walls, and contracts to pump blood; cells are bound together by intercalated discs and arranged around a fibrous skeleton that provides structural support for openings between heart chambers and vessels.

1.3 Smooth Muscle

• Smooth muscle: involuntary muscle found in walls of hollow organs (e.g., the digestive tract); not under conscious control.

2. Skeletal Muscle Organization

In skeletal muscle, muscle tissue is organized with layered connective tissues:

2.1 Connective Tissue Layers

• Endomysium around each muscle cell, fascicles wrapped by the perimysium, and the whole muscle encased by the epimysium. These connective tissue layers converge into a tendon, a dense regular connective tissue that attaches muscle to bone and forms a continuous chain into bone. Deep fascia wraps around muscle groups, dividing limbs into compartments and providing a framework for muscle function.

2.2 Vascularization of Muscle and Tendons

Skeletal muscle is richly vascularized, enabling efficient nutrient delivery and waste removal. However, tendons have relatively sparse blood supply, so tendinopathies heal slowly compared to more vascular tissues such as muscle.

3. Nervous System Control of Muscles

Nervous system input and control are essential to muscle function.

3.1 Voluntary and Involuntary Control

Skeletal muscle is under voluntary control via somatic motor neurons, while smooth and cardiac muscle are typically involuntary and regulated by the autonomic nervous system.

3.2 Autonomic Nervous System Divisions

The autonomic system is divided into two branches:

• Sympathetic nervous system (fight or flight): increases heart rate and force of contraction, dilates pupils, and redirects blood flow to essential areas during stress or danger.

• Parasympathetic nervous system (rest and digest): reduces heart rate, promotes digestion, and supports energy conservation.

Nervous System

1. Divisions of the Nervous System

1.1 CNS and PNS Definition

The nervous system is divided into the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS comprises the brain and spinal cord, while the PNS includes nerves that extend to the periphery.

2. Central Nervous System (CNS)

The CNS processes sensory information and generates motor responses.

2.1 Brain (Gray and White Matter)

In the brain, gray matter contains neuron cell bodies, while white matter contains axons that transport signals across regions.

2.2 Spinal Cord

The spinal cord features a butterfly-shaped gray matter core with surrounding white matter tracts and houses sensory and motor pathways.

3. Peripheral Nervous System (PNS)

3.1 Cranial and Spinal Nerves

The PNS consists of cranial nerves (12 pairs) and spinal nerves that connect to the CNS. The text gives examples such as the optic nerve (a cranial nerve) and the trigeminal nerve (cranial nerve V) which splits into three branches.

3.2 Nerve Organization

Nerves are organized in bundles: individual nerve fibers are surrounded by endoneurium; groups of fibers form fascicles wrapped by perineurium; and multiple fascicles are enclosed by the epineurium. Nerves carry sensory information toward the CNS and motor information away from it.

4. Neural Pathways and Integration

4.1 Sensory Input and Motor Output

A practical visualization: receptors detect stimuli (e.g., temperature), initiating action potentials that travel along sensory fibers to the spinal cord and brain, where they are interpreted as sensation. Motor information then travels from the brain back through motor pathways to effectors such as muscles, enabling actions.

4.2 Integration

The nervous system also integrates sensory input with motor output to regulate responses. A two-part look at the nervous pathways emphasizes the presence of both sensory input and motor output, along with integration, to complete the neural circuit.

5. Autonomic Nervous System

5.1 Functions and Divisions (Sympathetic/Parasympathetic)

In addition to voluntary skeletal muscle control, the autonomic nervous system regulates involuntary activities such as heart rate and digestion. The sympathetic “fight or flight” and parasympathetic “rest and digest” divisions coordinate cardiovascular, respiratory, and gastrointestinal responses according to the body’s needs.

Endocrine System

1. Overview and Function

The endocrine system is one of the body’s two main control systems (the other being the nervous system). It regulates activity more slowly and for longer durations through hormones released by endocrine glands into the bloodstream, binding to receptors on target cells to alter metabolism and function.

1.1 Hormonal Regulation

The endocrine system regulates activity more slowly and for longer durations through hormones released by endocrine glands into the bloodstream, binding to receptors on target cells to alter metabolism and function.

2. Endocrine Organs and Glands

Key endocrine organs discussed include:

2.1 Brain-Based Glands

• Hypothalamus and pituitary gland: situated close together; the hypothalamus communicates with the pituitary to regulate many hormones.

• Pineal gland: located midline in the brain; regulates circadian rhythms and sleep.

2.2 Neck Glands

• Thyroid gland: located below the thyroid prominence (Adam’s apple); regulates body temperature, metabolism, and energy levels. Goiter (an enlarged thyroid) is a well-known condition associated with thyroid dysfunction.

• Parathyroid glands: small glands posterior to the thyroid; regulate blood calcium levels essential for muscle and nerve function.

2.3 Thoracic and Abdominal Glands

• Thymus: situated in the thoracic cavity just superior to the heart and posterior to the manubriosternal joint; large in infancy and infantilized with age; important for immune cell development.

• Pancreas: located near the duodenum in the abdomen; produces digestive enzymes and ions to regulate pH; also central to glucose regulation via insulin and glucagon (relevant to diabetes).

• Adrenal glands: sit atop the kidneys; secrete hormones such as adrenaline (epinephrine) that prepare the body for stress responses.

2.4 Reproductive Glands

• Ovaries and testes: gonads of the female and male reproductive systems, regulating reproductive cycles and sperm production, respectively.

2.5 Central Regulatory Hub

This overview highlights how endocrine organs coordinate wide-ranging physiological processes, from growth and metabolism to immune function and reproduction. The hypothalamus–pituitary axis is a central regulatory hub for many hormonal cascades.

Cardiovascular System

1. Components and Blood Flow

1.1 Heart and Blood Vessels

The cardiovascular system includes the heart and blood vessels, circulating blood to deliver oxygen and nutrients and remove wastes such as carbon dioxide.

1.2 Unidirectional Flow

Blood flow is unidirectional and driven by the heart’s pumping action.

2. Blood Vessels

2.1 Arteries and Capillaries

Arteries carry blood away from the heart under high pressure, and as they branch into smaller vessels, pressure drops until reaching the capillaries, where nutrient and gas exchange occur across the capillary walls (which are only one cell thick).

2.2 Veins and Pressure

Veins return blood to the heart; the pressure in veins is much lower, so their walls are thinner and they rely on mechanisms like skeletal muscle pumps and one-way valves to prevent backflow.

3. Pulse Assessment Sites (Arteries)

A practical example of pulse assessment: the artery you palpate to check a pulse is typically an artery under higher pressure and hence deeper (protected by overlying tissues). Common palpation sites include:

3.1 Carotid Artery

• Carotid artery in the neck (near the thyroid prominence, the Adam’s apple): press laterally to the thyroid cartilage to feel a pulse. This artery supplies blood to the head and brain.

3.2 Brachial Artery

• Brachial artery in the upper arm, palpated at the anterior elbow by locating the biceps tendon and moving medially to locate the pulse.

3.3 Radial Artery

• Radial artery at the wrist (lateral to the radius) by locating the tendon of flexor carpi radialis and moving slightly lateral to feel the pulse.

3.4 Femoral Artery

• Femoral artery in the groin area, obtainable by locating the anterior superior iliac spine and the pubic bone and feeling inferior to the inguinal ligament.

3.5 Dorsalis Pedis Artery

• Dorsalis pedis artery on the dorsum of the foot by using the tendon of extensor hallucis longus as a landmark and palpating just distal to the ankle joint and lateral to the tendon.

4. Superficial Veins

Veins are superficial and have lower pressure, making them suitable targets for blood draws. The transcript notes superficial upper-limb veins such as:

4.1 Upper-Limb Veins

• Cephalic (lateral forearm/arm)

• Basilic (medial forearm/arm) veins

• Medium-grade median cubital vein in the anterior elbow region.

4.2 Lower-Limb Veins

In the lower limb, the great saphenous vein runs along the medial leg and thigh into the femoral vein, while the small saphenous vein runs laterally and drains behind the knee.

4.3 Varicose Veins

Varicose veins can occur due to stagnant venous blood from gravity with prolonged standing.

5. Heart Chambers and Valves

5.1 Heart Chambers

The heart itself consists of four chambers: right atrium, right ventricle, left atrium, and left ventricle.

5.2 Heart Valves

Between these chambers are four main valves: the tricuspid (between right atrium and right ventricle), the mitral (bicuspid) valve between the left atrium and left ventricle, the pulmonary valve (between the right ventricle and the pulmonary artery), and the aortic valve (between the left ventricle and the aorta).

6. Auscultation of Heart Valves

6.1 Auscultation Overview

Auscultation (listening to heart sounds) helps assess valve function.

6.2 Aortic Valve Auscultation

The aortic valve is best heard at the right of the sternum between the second and third ribs.

6.3 Pulmonary Valve Auscultation

The pulmonary valve is typically heard near the left second intercostal space.

6.4 Mitral Valve Auscultation

The mitral valve is best heard around the left midclavicular line at about the fifth intercostal space.

6.5 Tricuspid Valve Auscultation

The tricuspid valve is best heard along the left lower sternal border near the fifth intercostal space.

6.6 Integrated View of Cardiovascular System

• This integrated view of the cardiovascular system illustrates how the heart and vessels support a dynamic circulatory network, balancing high-pressure arterial flow with lower-pressure venous return and maintaining circulation for tissue perfusion, gas exchange, and metabolic waste removal. The notes highlight how structure reflects function—from thick-walled arteries to withstand pressure, to flexible veins with valves, to capillaries enabling exchange, and to pulses as a practical clinical tool for assessing circulation.