Human Body Cells PDF

# Human Body Cells ## Red Blood Cells - Red blood cells are responsible for delivering oxygen and removing waste from the body. - They contain a protein called hemoglobin, which is bright red and contains iron. - Hemoglobin bonds with oxygen in the lungs and releases it to cells throughout the body...

# Human Body Cells ## Red Blood Cells - Red blood cells are responsible for delivering oxygen and removing waste from the body. - They contain a protein called hemoglobin, which is bright red and contains iron. - Hemoglobin bonds with oxygen in the lungs and releases it to cells throughout the body. - Red blood cells also bond with carbon dioxide and other waste products to transport them away. - The lifespan of a red blood cell is 120 days. - Red blood cells are constantly being replaced by new cells produced in the bone marrow. - Mature red blood cells are flexible and lack a nucleus and most organelles. ## White Blood Cells - White blood cells (WBCs) or leukocytes, fight infection. - The average adult has 4,000 to 10,000 WBCs per microliter of blood. - An increase in this number indicates infection. - The six main types of WBCs are: - Neutrophils (58%) - Eosinophils (2%) - Basophils (1%) - Bands (3%) - Monocytes (4%) - Lymphocytes (4%) - **Neutrophils** are the body's main defense against bacteria. - They kill bacteria by ingesting them, a process called phagocytosis. - Neutrophils can ingest 5-20 bacteria in their lifetime. - **Eosinophils** kill parasites and play a role in allergic reactions. - **Basophils** release histamine, which dilates blood vessels and attracts WBCs, and heparin, which thins blood. - **Monocytes** enter tissues where they develop into macrophages, which engulf bacteria, old cells, and cellular debris. - Macrophages reside in the liver, spleen, lungs, lymph nodes, skin, and intestines. - **Lymphocytes** play a key role in the immune response. ## Skin Cells - The skin is the largest organ of the body and serves as a protective barrier. - The skin consists of four layers: - **Epidermis:** the outermost layer, 0.2mm thick. It consists of dead cells being shed and new cells growing to replace them. - It takes approximately 28 days for a new cell to reach the surface. - **Basement membrane zone:** located between the epidermis and dermis. - **Dermis:** 1.8mm thick, composed of collagen and elastin. - It contains blood vessels, nerves, oil and sweat glands, pores, and hair follicles. - **Subcutaneous layer:** - The functions of the skin include: - Protection against friction, chemicals, UV radiation, and particles - Protection against infection - Prevention of water loss - Synthesis of vitamin D - Temperature regulation - Sensation (pain, touch, and temperature) - Wound healing - Antigen presentation and immunological response ## Bone Cells - Bone growth and repair is orchestrated by a specialized group of cells. - Mesenchymal stem cells develop into: - **Osteoblasts:** produce new bone by binding together to form **osteoid,** which is a combination of protein and collagen. - Osteoblasts facilitate the uptake of minerals like calcium to form the bone's outer surface. - **Osteoclasts:** large cells that dissolve bone and release its calcium into the bloodstream. - Osteoclasts have multiple nuclei. - **Osteocytes:** originate from osteoblasts, reside underneath the bone surface, and send out long connectors to communicate with other bone cells. - Osteocytes sense damage to the bone and activate osteoclasts and osteoblasts to repair it. ## Muscle Cells - Muscle cells produce movement and maintain posture by contracting. - There are three types of muscle: - **Skeletal muscle:** attached to bone and responsible for voluntary movement. - Skeletal muscle cells appear striated. - They have multiple nuclei and numerous mitochondria. - **Cardiac muscle:** found only in the heart. - It has striations that are less organized than those found in skeletal muscle. - The cells are often branched and communicate with one another. - Cardiac muscle is generally involuntary. - **Visceral muscle:** lines blood vessels and internal organs. - Visceral muscle is not striated. - The cells are short and typically have one nucleus. - Visceral muscle is also generally involuntary. ## Sperm Cells - The sperm cell is the male reproductive cell. - It contains the male chromosomes (DNA) in its nucleus, which combines with the female egg's chromosomes during fertilization. - The sperm cell has three parts: - **Head:** contains the nucleus and a cap called the **acrosome,** which is filled with enzymes needed to penetrate the egg. - **Midpiece:** contains mitochondria, which provide energy for the sperm's journey to the egg. - **Tail:** flagellating tail that propels the sperm cell. - Human sperm cells are typically 10 micrometers long. - In comparison to plants, human sperm cells carry much more DNA. - Human sperm cells can survive for up to three days within the female reproductive system, but many die off quickly, within minutes or hours. ## Fat Cells - Fat cells are important for storage and regulation of body functions. - There are two types: - **White fat cells:** store extra fat. - **Brown fat cells:** produce heat, and are primarily found in babies but may be present in adults. - Functions of fat cells include: - **Warmth:** providing insulation. - **Protection:** surrounding and protecting vital organs. - **Storage:** storing extra fat. - **Regulation of body functions:** regulating the metabolism of stored fat. - **Smoothing:** filling the spaces between muscles and bones, contributing to a smoother body shape. ## Nerve Cells - A nerve cell, or **neuron**, is the basic unit of the nervous system. - Neurons transmit information to and from the brain. - There are three main types of neurons: - **Motor neurons:** send information from the brain to muscles and glands. - **Sensory neurons:** send information from the body to the brain. - **Interneurons:** connect neurons within the brain and spinal cord. - A neuron consists of: - **Cell body:** contains the nucleus and other cell parts. - **Axon:** a long extension that carries information away from the cell body. - **Dendrites:** branching extensions that receive information from other neurons. - Information is transmitted through the axon as an electrical signal. - At the end of the axon, the signal is released as a chemical signal called a **neurotransmitter,** which crosses the **synapse** (the gap between neurons) and triggers a response in the next neuron.