Human Biology - Lec. 6 Digestive System & Skin PDF

Human Biology Lec.6 Digestive system &Skin Digestion: Is the process by which the large complex molecules in food are broken down into smaller molecules that can be used by the body. The digestive system includes the gastrointestinal tract is composed of: (Mouth...

Human Biology Lec.6 Digestive system &Skin Digestion: Is the process by which the large complex molecules in food are broken down into smaller molecules that can be used by the body. The digestive system includes the gastrointestinal tract is composed of: (Mouth, oro- pharynx, esophagus, stomach, small intestine and large intestine) and the associated glands (salivary glands, liver, gall bladder, and Pancreas) Ingestion: the process of taking in food into the digestive tract through an opening, usually called a mouth is known as ingestion. Digestion consists of two types of processes Mechanical breakdown: The process of breaking down food into smaller pieces by teeth and tongue mixed food with saliva contains bacteria killing enzyme and antibodies). Also the mucus help food to move from throat to stomach using muscle movement called peristalsis. Chemical breakdown: The particles of food are acted upon by enzymes that break them down into simpler subunits. Digestion in Stomach  Stores food and releases it gradually into the small intestine, Stomach helps in the mechanical breakdown of large pieces of food and Chemical breakdown  Gastric fluid includes: 1-Pepsinogen (inactive Pepsin Proteins Peptides). 2-HCL  Activates inactive pepsinogen into active pepsin  Kills bacteria.  Makes the medium acidic which is suitable for pepsin to act on proteins. 3-The stomach secretes a layer of mucus to protect itself from its own acidic. Sphincters: circular muscles help food movement in and out stomach (pyloric &cardiac)   Digested juices and enzymes turn the partly digested food in the stomach into a semi liquid mixture called chyme  Food takes six hours to empty the stomach after a meal. Water & alchohol will be absorbed in stomach The main function of small intestine is to digest food and absorb the digested food into the blood stream with liver and pancreas. Absorption occur in small and large intestine  Small intestine include bile juice, pancreatic juice, and digestive enzymes 1-bile juice: Liver secretes bile which is stored in the gall bladder and released when needed through the bile duct, Bile helps in emulsification of fats 2-pancreatic juice : neutralizes the acidic chyme and enzyme digests carbohydrates, proteins and lipids.  Pancreatic proteases(trypsin ): break down protein into peptides , Pancreatic lipases break down fats into fatty acid and glycerol 3-Digestive Enzymes The walls of the small intestine secrete digestive enzymes to digest food Peptidases to split small peptides into amino acids Maltase acts on maltose and converts it into glucose Sucrase acts on sucrose and converts it into glucose and fructose. Lactase acts on lactose and converts it into glucose and galactose Lipases acts on lipids and convert it into fatty acid and glycerol   The small intestine has numerous folds and projections (Villi ) that give it an internal surface area Villi : Minute finger like projections cover the entire folded surface of the intestinal wall. Each individual cell of the villi bear microscopic projections called microvilli  Each villus of the small intestine is provided with a rich supply of blood capillaries that absorbed nutrient except large fat molecules and distribute them throughout the body. Nutrients absorbed by the small intestine include water, monosaccharides , amino acids and short peptides, fatty acid produced by lipid digestion, vitamins and minerals. Elimination/egestion: In digestable materials must be expelled from the body. The end of the large intestine is the rectum short term storage which holds feces before it is expelled Large intestine It has two parts, colon and rectum. The large intestine has bacteria which live on unabsorbed food, the intestinal bacteria can synthesize vitamin B 12 , thiamin, and Vitamin K.  Cells lining the large intestine absorb these vitamins and water , salts and concentrate waste After absorption is complete, any remaining material is converted into semisolid feces. Accessory gland 1-Pancrease: organ secreted enzyme &hormones Amylase,Trypsin, lipase insulin &glucagon 2-liver: organ effects on digestion by producing bile Regulate cholesterol by bile salts (green fluid) blood, store iron , vitamins A D E K 3-Gall bladder: Structure located near liver , store the bile ,bile will break fats and make it emulsifies The skin (also known as the cutis or integument) serves as the main cover of the body. The skin is considered the largest organ of the body and weights up to 16% of total body weight. The skin consists of two main layers : Epidermis (of ectodermal origin): The epidermis consists of stratified squamous epithelium with a layer of keratin. 4 cell types, with different embryologic origins, are distinguished in the epidermis: Keratinocytes (keratin production) Melanocytes (pigment production) Langerhans cells (immune system) Merkel cells (diffuse neuroendocrine system).  Dermis (derived from mesoderm): is the layer of connective tissue beneath the epidermis. Two distinct regions are present in the dermis:- papillary layer reticular layer The papillary layer includes the area of the dermal papilla and consists of loose connective tissue. The main blood vessels that supply the epidermis are located in the papilla. The reticular layer is thicker than the papillary layer and consists of a more dense, irregular connective tissue composed mainly of collagen bundles. The term reticular refers to the netlike arrangement of these bundles.  The Hypodermis is a subcutaneous layer, composed mainly of adipose tissue and loose connective tissue. The border between the epidermis and dermis is distinct and consists of a series of ridges (epidermal ridges) and papillae (dermal papillae). Skin appendages (derived from epithelium) include: o hair o nails o exocrine glands (sweat glands, sebaceous glands) Functions of skin  Mechanical protection. The stratified keratinous epithelium of the skin provides protection against external abrasions or injury and against invasion of foreign objects.  Thermoregulation.  Osmoregulation. The skin is important in the regulation of body fluids and ions, and also protects against fluid loss.  Excretion and secretion. The skin possesses exocrine glands (sweat glands, sebaceous glands). Sensory reception: Metabolic functions. The prohormone of vitamin D is present in the skin and is stimulated by ultraviolet light to provide the initial stage of the pathway leading to the synthesis of vitamin D metabolites. Absorption. Various substances, including many drugs, can be absorbed through the skin (transdermal absorption). This is common today with nitroglycerine (for cardiac therapy), estrogen (for postmenopausal replacement) or drugs to counter motion sickness. Glands of the skin : 1- Sweat gland : formed of 2 two parts : a- Glandular part. b- Secretory part. ( duct part ) This gland is simple tubular coiled gland , glandular part is formed of two columnar to cuboidal cells , duct part is formed of double layer of cuboidal cells ( stratified cuboidal ). 2- Sebaceous glands : found in association with hair follicle , this gland secrete a sebum which is a lipoprotein in material.