Cell Structure and Function PDF

# Cell structure and function - Cells are the building blocks of the human body. About trillions human body cells form and maintain anatomical structures, and they perform physiological functions. - **Cell anatomy:** A cell is surrounded by extracellular fluid. the cells outer boundary called the...

# Cell structure and function - Cells are the building blocks of the human body. About trillions human body cells form and maintain anatomical structures, and they perform physiological functions. - **Cell anatomy:** A cell is surrounded by extracellular fluid. the cells outer boundary called the cell membrane, separates the cytoplasm, or the cell contents, from the extracellular fluid. ## The Organelles - The cell contains specialized structures called Organelles, which means "Little organs" that perform different functions. - Because cells vary so greatly in size, shape, content, and function, describing a "typical" cell is impossible. - In reality, cells have most, but not all of these Organelles structures. ### 1- Cytoplasm - The main substance that fills the cell and holds the organelles is the cytoplasm. ### 2- Nucleus - It is the largest organelle. This is often called the control center of the cell because it contains the genetic material, which controls all of the activities of the cell, including cell reproduction. ### 3- Endoplasmic Reticulum (ER) - ER is a complex organelle composed of membrane bound, flattened sacs, elongated canals, and fluid-filled sacs. These membranous parts are interconnected and communicate with the cell membrane, the nuclear envelope, and other organelles. - The area of the ER to which ribosomes are attached are described as "Rough Endoplasmic Reticulum", where no ribosomes are attached, the ER is described as "Smooth Endoplasmic Reticulum". - The ribosomes of rough ER are sites of protein synthesis. The proteins may then move through ER tubules to the Golgi apparatus for further processing. - Smooth ER contains enzymes important in lipid synthesis. ### 4- Ribosomes - Many ribosomes are attached to Endoplasmic Reticulum (ER) membranes, there are scattered throughout the cytoplasm. - All ribosomes are composed of protein and RNA molecules. Ribosomes as well as a structural support for the RNA molecules that come together as the cell synthesizes proteins from amino acids. ### 5- Golgi apparatus - The Golgi apparatus is composed of a stack of about six flattened, membranous sacs. This organelle refines, packages, and delivers proteins synthesized on ribosomes associated with the ER, and secretion is out the cell. ### 6- Mitochondria - Are round or bean-shaped structures with folded membrane on the inside. - Within the mitochondria, food is converted to energy for the cell in the form of ATP. ### 7- Centrioles - Rod-shaped bodies near the nucleus that function in cell division. ### 8- Lysosomes - Which contain digestive enzymes. - Some cells have small, hair like projections from the surface called "Cilia", which wave to create movement around the cell. - A long, whiplike projection from the cell is flagellum. ### 9- Cell membrane - This membrane is the outer layer of the cell. It consists of a double layer of phospholipid molecules (each one includes a hydrophilic phosphate group (soluble in water) and two hydrophobic fatty acids (insoluble in water)) with proteins scattered throughout the lipid bilayer and small amount of carbohydrates. - The proteins may act as: * **Receptors**: for extracellular compounds * **Carriers**: for materials into or out of the cell. ## Movement of Substances Across Cell Membrane - The cell membrane is very important in regulating what can enter and leave the cell. - The permeability of the cell membrane: - is the property that determines which substance can enter or leave the cytoplasm. - Our cell membranes are selectively permeable (semi-permeable), permit the passage of some materials and stop the passage of others. - **Membrane transport** Movement across the membrane may be passive or active. ### A. Passive processes - Move ions and molecules across the cell membrane required no energy such as; 1- diffusion, 2- filtration ### B. Active processes - Move ions and molecules across the cell membrane required energy such as; active transport. #### 1- Diffusion - Is the movement of a small molecules or ions from area of higher concentration to area of lower concentration. (require no energy). Ex: exchange of gases (O₂ or CO₂) in the lungs or body tissues. #### Osmosis - It is a special type of diffusion. It is diffusion of water across a membrane in response to differences in concentration. The force of water movement is osmotic pressure. - Solutions of various solute concentration are described as isotonic, hypertonic, or hypotonic solution with regard to their effects on the shape or tension of the plasma membrane of living cells: * **Isotonic solution**: water move in and out the cell membrane equally. * **Hypertonic solution**: water move outside the cell "shrinking of cell". * **Hypotonic solution**: water move inside the cell "cell burst-hemolysis". #### 2- Filtration - Movement of water and materials through cell membrane under mechanical force. The passage of water containing dissolved materials through a membrane as a result of a mechanical (pushing) force on one side: - Ex: the formation of urine in the microscopic functional units of the kidney. #### Active Transport - Movement of molecules from area of lower concentration to area of higher concentration. - This movement, because it is against the natural flow, requires energy in the form of ATP. It also requires proteins in the cell membrane that act as carriers from the molecules. Because the cell membrane can carry on active transport, it most accurately described as selectively permeable. It regulates what can enter and leave the cell based on the needs of the cell. - Ex: 1. Absorption of amino acids and glucose from food by the cell of the intestine. 2. Sodium and potassium pumps in muscle and nerve cells. ## Vesicular transport - Materials move into or out of a cell in membranous sacs that form at, or fuse withcell membrane. Two types are present endocytosis and exocytosis. #### 1. Endocytosis - Movement of extracellular material by forming a vesicle at the cell surface into the cell such as: ##### A. Receptor-mediated endocytosis - An active process includes receptor at the surface membrane which can bind with specific molecules then forming vesicles to betransported into the cells. ##### B. Phagocytosis - "Cell eating" cell engulfing of large particles by cell membrane. - Ex: White blood cells phagocytic bacteria. ##### C. Pinocytosis - "Cell drinking" cell engulfing of smaller particles and dropletsof extracellular fluid. Ex: cells of the kidney tubules reabsorb small proteins. #### 2. Exocytosis - The functional reverse of endocytosis. In exocytosis, a vesicle created inside the cell fuses with the cell membrane and discharges its contents into extracellular environment. Contents may be "hormones, mucous, or waste products". ## The Integumentary system - Consist of the skin, hair, nails, and various glands. ### Integumentary structure & function - **Structure:**- Integument have two components: * The cutaneous membrane * The accessory structure - **Function:** #### 1- The cutaneous membrane - Skin consist from * **Epidermis:** which contains 5 layers. Thin epidermis have only 4 layers (0.08mm thickness), and thick epidermis layer (0.5 mm thickness). * **Dermis:** consists from loose connective tissue. * **Hypodermis (subcutaneous layer):** another layer exists under skin layer, and consists from loose connective tissue. #### 2- The accessory structure - Consist from * Hair, nail, and variety of exocrine glands. ### Integumentary (skin) function - **Protection:** the skin covers & protects underlying tissues & organs from impacts, chemicals, and infections, & it prevents the loose of body fluids. #### Thermoregulation (Temperature maintenance) - The skin maintains normal body temperature by regulating heat exchange with the environment. #### 3. Synthesis and storage of nutrients - The stratum germinativum of epidermis synthesizes vitamin D3, a steroid building block for a hormone that aids calcium uptake. The dermis stores large reserves of lipids in adipose tissue. #### 4. Sensory reception - Receptors in the integument detect touch, pressure, pain, and temperature stimuli and rely that information to the nervous system. #### 5. Excretion & secretion - Integumentary glands excrete salts, water, and organic wastes. #### A. The Epidermis - It consists of a stratified squamous epithelium of several different cell layers called strata (the deepest layer is stratum germinativum, spinosum, granulosum, lucidum (exist in palms & soles) and the most superficial layer is corneum. - **Large stem cells**, or germinative cells dominate the stratum germinativum, making it the layer where new cells are generated and begin to grow. The divisions of these cells replace cells that are lost at the epithelial surface. - The stratum germinativum also contain **melanocytes**, cells whose cytoplasmic processes extended between epithelial cells in this layer, which synthesize melanin, a brown, yellow-brown, or black pigment that colors the epidermis, and receptors that provide information about objects touching the skin. - Going to the surface the cells start to package with a large amount of protein called keratin. Keratin is extremely durable and water-resistant. So, the cells in the outer layer are **dead epithelial cells**. #### B. The Dermis - The dermis lies under the epidermis. It has to major components: a superficial papillary layer and a deeper reticular layer. ##### 1. The papillary layer - Named after dermal papillae, consists of loose connective tissue that support and nourishes the epidermis. This region contains blood and nerves supplying the surface of the skin. ##### 2. The deeper reticular layer - Consists of interwoven meshwork of dense, irregular connective tissue. The elastic fibers provide flexibility, and the collagen fiber limit that flexibility to prevent damage to the tissue. ##### 3. Other dermal components - In addition to above mention, the dermis contains the mixed cell populations of connective tissue proper. Epidermal accessory organs, such as hair follicles and sweat gland, extend into the dermis. #### Hypodermis (subcutaneous tissue) - It consists of loose connective tissue with many fat cells. It serves as energy reserve, reduced heat loss, and it attached the skin with the underlying tissue and organ "muscle and bone" #### 2- Accessory structure - Accessory structure includes hair and hair follicles, sebaceous glands, sweat glands, and nails. # The skeletal system - The skeletal system contains 206 separated bones. - The skeletal system includes the bones and the cartilages, joints, ligaments, and other connective tissues that stabilize or connect them. ### This skeletal system has five primary functions: - **Support**: it provides structural support for the entire body. Individual bones or groups of bones provide a framework for the attachment of soft tissues and organs. - **Storage**: the calcium salts of bone represent a valuable mineral reserve that maintains normal concentrations of calcium and phosphate ions in the body fluids. In addition, bones store energy reserves as lipids in areas filled with yellow marrow. - **Blood cell production**: red blood cells, white blood cells, and other blood elements are produced within the red bone marrow. - **Protection of soft tissues and organs are often surrounded by skeletal elements.** The ribs protect the heart and lungs, the skull encloses the brain, the vertebrae shield the spinal cord. - **Movement due to attached skeletal muscles.** ### 1-The structure of bone - The bone is a supporting connective tissue that contain specialized cells and a matrix consisting of extracellular protein fiber and ground substance. - The distinctive texture of bone results from the deposition of calcium salts within the matrix. Calcium phosphate, Ca3(PO4)2, account for almost two-thirds of the weight of the bone. The remaining third is dominated by collagen fibers. Osteocytes and other cell type make up only around 2% of the mass of a bone. - The bones have four general shapes: long, short, flat, and irregular. - Two type of bones are exist: * **Compact bone (solid).** * **spongy bone (cancellous)** a network of bone rods separated by space. - **Long bones have:** * diaphysis (bone shift). * epiphysis * bone marrow - **Bone covers:** * **A-Periosteum**: the outer surface bone covered, its functions: * Attach skeletal muscles to bones. * Isolates the bone from surrounding tissues. * Provides a route for circulatory and nervous supplies. * Participate in bone growth and repair. * **B-Endosteum**: lines the marrow cavity and other inner, its function: * Its active during bone growth and whenever repair or remodeling is under way. ### The cells in bone - **Osteocytes** are the most abundant cells in bone, other cell types are also present as osteoclasts and osteoblasts. - Osteocytes are mature bone cells. Osteocytes maintain bone structure by recycling the calcium salts in bone matrix around themselves & by assisting in repairs. - **Osteoclasts** are giant cells with 50 or more nuclei. Acids and enzymes secreted by osteoclasts dissolve the bony matrix and release the stored minerals through osteolysis, or resorption. This process helps regulate calcium and phosphate concentrations in body fluids - **Osteoblasts** are the cells responsible for the production of new bone, a process called osteogenesis. Osteoblasts produce new bone matrix and promote the deposition of calcium salts in the organic matrix. ### Requirements for normal bone growth - Normal bone growth and maintenance require the following: * **Calcium and phosphate salts**, the body must be able to absorb and transport these minerals to sites of bone formation. * **Vitamins D3, A, C.** * **Hormones including growth hormone, thyroid hormone, etc** ### Bone remodeling and homeostatic mechanisms - It's the process of continually removing and replacing calcium salts and surrounding matrix through activities of osteocytes, osteoblasts, and osteoclasts. The turnover rate for bone is quite high, and in adults roughly 18% of the protein and mineral components are removed and replaced each year through the process of remodeling. ### Bone Injury and repair - Bone fractures develops when bones are subjected to extreme loads. Bone will heal even after they have been severely damaged by 4 steps, if the periosteum & endosteum are survive : * **Step 1 - formation of fracture hematoma.** * **Step 2 - formation of internal and external callus.** * **Step 3 - osteoblasts replace the new central cartilage of external callus with spongy bone.** * **Step 4 - the remodeling process of spongy bone at the site of fracture which may continue over a period of 4 months to well over a year.** ### Bone of the human body - The skeletal system contains 206 separated bone. * 22 bones in skull. * 6 in middle ears. * 1 hyoid bone. * 33 in vertebral column. * 24 in thoracic cage. * 60 in upper limbs. * 60 in lower limbs. ### The skull - **Cranium**: 8 sutured bones in cranium. - **Facial bones**: 13 sutured bones, 1 mandible. ### Articulation (joints) - Joints: are the point of meeting between two bones. * Joints exist wherever two bones meet. * Structure of joints determine the type of movement. ## Axial skeleton - **Skull (22)** - **Cranium**: 8 - **Face**: 14 - **Skull and associated bones (29)** - **Associated bones (7)** - Auditory ossicles: 6 - Hyoid: 1 - **Thoracic cage (25)** - **Sternum (1)** - **Ribs (24)** - **Vertebral column (26)** - **Vertebrae (24)** - **Sacrum (1)** - **Coccyx (1)** ## Appendicular skeleton - **Pectoral girdle (4)** - **Clavicle (2)** - **Scapula (2)** - **Upper limbs (60)** - **Humerus (2)** - **Radius (2)** - **Ulna (2)** - **Carpal bones (16)** - **Metacarpal bones (10)** - **Phalanges (proximal, 28 middle,distal)** - **Pelvic girdle (2)** - **Coxal bone (hipbone) (2)** - **Lower limbs (60)** - **Femur (2)** - **Patella (2)** - **Tibia (2)** - **Fibula (2)** - **Tarsal bones (14)** - **Metatarsal bones (10)** - **Phalanges (28)**