Sheet #6. Dr. Heba Kalbouneh. Dr. Heba Kalbouneh. Dr. Heba Kalbouneh

Transcription

1 Sheet #6 Dr. Heba Kalbouneh Dr. Heba Kalbouneh Dr. Heba Kalbouneh

2 Ducts - In large glands, as you go away from the secretory unit, the duct becomes larger and the lining epithelium becomes thicker (from cuboidal to columnar and from simple to stratified) - Excretory ducts: are generally passive conducting tubes - Larger excretory ducts may be lined by stratified cuboidal or columnar epithelium. Myoepithelial cells - Located between the secretory cells and the basement membrane - Rich in actin and myosin (contractile proteins) - When these cells contract, they squeeze the secretory cells and ducts, helping to extrude the contents. Classification according to the type of secretion: 1. Mucous glands: These glands produce a viscid, slimy, carbohydrate-rich secretion which is called mucus, e.g; the goblet cells. 2. Serous glands: These glands produce thin, watery, protein-rich secretions, often high in enzymatic activity, e.g; the parotid salivary gland.

3 3. Mixed (seromucous or mucoserous) glands: These glands produce both mucous and serous secretions. e.g; the sublingual and submandibular salivary glands. Note: the salivary glands that produce saliva inside the oral cavity are: Parotid (serous) Sublingual (mucoserous) Submandibular (seromucus) Classification according to the mode of secretion (how these cells release their product): Merocrine glands: The secretory product is delivered in membrane-bounded vesicles (secretory vesicles) to the apical surface of the cell. Here, vesicles fuse with the plasma membrane and extrude their contents by exocytosis e.g; pancreas, salivary glands (note: most glands in our body secret by merocrine mode of secretion) Apocrine glands: In these glands part of the apical cytoplasm is lost along with the secretory material. e.g; lactating mammary glands, special sweat glands located in axilla and perianal area and the ceruminous glands (wax glands) of the external auditory tube.

4 Holocrine glands: In these glands the entire cells laden with secretory material disintegrate and all of the cellular contents are discharged from the gland as secretions e.g; the sebaceous glands of skin. So we have many classifications for the glands For example, the sebaceous glands are exocrine sebum secreting glands, holocrine glands, and simple branched acinar gland Sebaceous gland is a small gland in the skin which secretes a lubricating oily matter (sebum) into the hair follicles to lubricate the skin and hair. Acne often begins during puberty. It occurs when sebaceous glands in the skin are over-stimulated to produce sebum due to hormonal factors. The increased production of sebum can lead to a blockage of the sebaceous gland duct. This can cause a comedo (blackhead) Sweat glands We have about 3 million sweat glands distributed on our skin. There are two types. Eccrine (merocrine) sweat glands are distributed all over our body and the ducts of these glands open into the surface, they produce true sweat and are the most numerous of the sweat glands, and are abundant on the palms of the hands, soles of the feet, and forehead; their secretion is clear watery secretion with electrolytes and it is filtration from the blood plasma also it s Hypotonic (lesser salt concentration) What is the main function of sweating? To cool the body temperature by evaporation

5 Apocrine sweat glands: they are in restricted places like the axilla or the genitalia. In human, their role is not really understood well.. but they are important in sexual attraction between animals The secretion of apocrine sweat glands is rich in proteins and lipids and this is called pheromones The secretion of apocrine sweat glands is associated with the presence of the hair follicle. Sweat has no odor but because it is exposed to bacterial decomposition, it becomes smelly. For example, your feet sweat into your shoes all day so they get wet and bacteria start to grow. The bacteria continue to breed once you've taken your shoes off, especially if you put them in a dark cupboard. Then, when you put your shoes back on the next day, even if you've just had a shower, putting your feet into still wet shoes creates the perfect conditions for the bacteria to thrive warm, dark and moist The structure of the sweat gland: simple coiled tubular gland Body membranes Membranes are thin layers of epithelial tissue with the underlying layer of connective tissue. Membranes cover, protect, or separate other structures or tissues in the body. The three types of membranes are: 1) cutaneous membranes; 2) serous membranes; 3) mucous membranes The cutaneous membrane is skin. Skin consists of a layer of stratified squamous epithelium (epidermis) firmly attached to a thick layer of

6 connective tissue (dermis). It differs from other membranes because it is exposed to air and is dry. The serous membranes (or serosae) consist of simple squamous epithelium (a mesothelium) supported by a layer of connective tissue. These moist membranes line the closed internal body cavities. The three types of serous membranes are: 1) the pleura, lining the pleural cavities and covering the lungs; 2) the peritoneum, lining the peritoneal cavity and covering the abdominal organs; and 3) the pericardium, lining the pericardial cavity and covering the heart. The mucous membranes (or mucosae) consist of epithelial tissue (usually stratified squamous or simple columnar epithelia) on a layer of connective tissue called the lamina propria (from the Latin, meaning one s own layer ). The mucosae line the body cavities that open to the exterior, such as the digestive, respiratory, reproductive, and urinary tracts. These membranes are kept moist by bodily secretions.