CHAPTER OUTLINE
11.1 Types of Tissues
Tissues are composed of similarly specialized cells that perform a common function in the body. The tissues of the human body can be categorized into four major types: epithelial tissue, connective tissue, muscular tissue, and nervous tissue.
Epithelial Tissue
Epithelial tissue consists of tightly packed cells that form a continuous layer. Epithelial tissue covers surfaces and lines body cavities. It usually has a protective function but it can also be modified to carry out secretion, absorption, excretion, and filtration.
Junctions between Epithelial Cells
The cells of a tissue can function in a coordinated manner when the plasma membranes of adjoining cells interact. Three common types of junctions link epithelial cells: tight, gap and adhesion junctions.
Connective Tissue
Connective tissue binds organs together, provides support and protection, fills spaces, produces blood cells, and stores fat. As a rule, connective tissue cells are widely separated by a matrix, consisting of a noncellular material.
Loose Fibrous and Dense Fibrous Tissues
Loose fibrous connective tissue supports epithelium and also many internal organs. Tendons and ligaments are made up of dense fibrous connective tissue, which contains many collagen fibers that are packed together. Loose and dense fibrous connective tissues have cells called fibroblasts.
Adipose Tissue and Reticular Connective Tissue
In adipose tissue, the fibroblasts enlarge and store fat. Reticular connective tissue forms the supporting meshwork of lymphoid tissue.
Cartilage
Cartilage is a specialized form of dense fibrous connective tissue, which most commonly forms the smoothsurfaces that allow bones to slide against each other in joints. There are three types of cartilage, distinguished by the type of fiber in the matrix: hyaline, elastic, and fibrocartilage.
Bone
Bone is the most rigid connective tissue. It consists of an extremely hard matrix. Compact bone makes up the shaft of a long bone, while the ends of a long bone contain spongy bone.
Blood
Blood is unlike other types of connective tissue in that the matrix is not made by the cells. The upper, liquid layer of blood is called plasma and make up about 55% of the volume of whole blood. Red blood cells carry oxygen to tissues; white blood cells fight infection. Platelets are involved in clotting.
Muscular Tissue
Muscular tissue is composed of cells called muscle fibers that contain actin and myosin filaments whose interaction accounts for movement. There are three types of muscle tissue: skeletal, smooth, and cardiac.
Nervous Tissue
Nervous tissue contains nerve cells called neurons and is present in the brain and spinal cord. The nervous system has just three functions: sensory input, integration of data, and motor output.
Neuroglia
In addition to neurons, nervous tissue contains neuroglia. Their primary function is to support and nourish neurons.
11.2 Body Cavities and Body Membranes
The human body can be divided into two main body cavities: the ventral cavity and the dorsal cavity. The ventral cavity is divided into the thoracic, abdominal, and pelvic cavities, while the dorsal cavity can be divided into the cranial cavity and vertebral canal.
Body Membranes
Body membranes line cavities and the internal spaces of organs and tubes that open to the outside. There are different types including mucous membranes, serous membranes, synovial membranes, and the meninges.
11.3 Organ Systems
Organ systems work together in the body. While a particular organ may be assigned to one system, it may assist in the function of other organ systems.
Integumentary System
The integumentary system contains the skin. It has a protective function, synthesizes vitamin D, collects sensory data, and helps regulate body temperature.
Cardiovascular System
The cardiovascular system consists of the heart, the blood, and the vessels that the blood moves through. Blood transports nutrients and oxygen and removes waste molecules, it is also a route by which cells of the immune system can be distributed throughout the body.
Lymphatic and Immune Systems
The lymphatic system protects the body from disease by purifying lymph and storing lymphocytes. The immune system consists of all the cells in the body that protect us from disease.
Digestive System
The digestive system includes the mouth, esophagus, stomach, small intestine, and large intestine, along with associated organs. It receives food and digests it into nutrient molecules.
Respiratory System
The respiratory system consists of the lungs and the tubes that take air to and from them. The respiratory system moves oxygen and carbon dioxide.
Urinary System
The urinary system contains the kidneys, the urinary bladder, and the tubes that carry urine. The system rids the body of metabolic wastes.
Nervous System
The nervous system consists of the brain, spinal cord, and associated nerves that allow us to respond to both external and internal stimuli.
Musculoskeletal System
Within the musculoskeletal system, the bones provide a scaffolding that helps hold and protect body parts. The skeleton also helps move the body, stores minerals, and produces blood cells.
Endocrine System
The endocrine system consists of the hormonal glands, which secrete chemical messengers called hormones that have a wide range of effects.
Reproductive System
The reproductive system has different organs in the male and female. It is responsible for the production of sex cells that fertilize and develop into offspring.
11.4 Integumentary System
The skin and its accessory organs (nails, hair, oil glands, and sweat glands) are collectively called the integumentary system.
Regions of the Skin
The skin has two regions: the epidermis and the dermis. The epidermis is made up of epithelium. The dermis is a region of fibrous connective tissue beneath the epidermis.
Accessory Organs of the Skin
Nails, hair follicles, and glands are structures of epidermal origin, even though some parts of hair and glands are largely found in the dermis.
Disorders of the Skin
The integumentary system is susceptible to a number of diseases.
11.5 Homeostasis
Homeostasis is the maintenance of a relatively constant internal environment by an organism.
Negative Feedback
Negative feedback is the primary homeostatic mechanism that keeps a variable close to a particular value, or set point. A homeostatic mechanism has at least two components: a sensor and a control center.
Mechanical Example
A home heating system is often used to illustrate how a more complicated negative feedback mechanism works.
Human Example: Regulation of Body Temperature
The sensor and control center for body temperature are located in a part of the brain called the hypothalamus. Negative feedback keeps human body temperature at around 98.6oF.
Positive Feedback
Positive feedback is a mechanism that brings about an ever greater change in the same direction.
Homeostasis and Body Systems
All systems of the body contribute toward maintaining homeostasis.
The Transport Systems
The cardiovascular system and lymphatic system regulate tissue fluid composition.
The Maintenance Systems
The respiratory system adds oxygen to and removes carbon dioxide from the blood. The digestive system takes in and digests food, providing nutrient molecules. The liver and kidneys help remove toxins from the blood. The urinary system excretes waste molecules and also regulates blood volume, salt balance, and pH.
The Support Systems
The integumentary, skeletal, and muscular systems protect the internal organs.
The Control Systems
The nervous system and the endocrine system work together to control other body systems so that homeostasis is maintained.
Disease
A disease is an abnormality in the body’s normal processes that significantly impairs homeostasis.
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