Epithelia and Glands Flashcards
What are mucous membranes?
Mucous membanes line internal tubes which open to the exterior
What are some examples of where mucous membranes are found?
Alimentary tact, respiratory tract and urinary tract - these bear mucous-secreting cells
What does a mucous membrane consist of?
- An epithelium
- An adjacent layer of connective tissue called the LAMINA PROPRIA
- In the alimentary tract, a third layer of smooth muscle (THE MUSCULARIS MUCOUSAE)
What is the layer of connective tissue in a mucous membrane called?
Lamina propria
What is the layer of smooth muscle in the mucous membrane of the alimentary tract called?
Muscularis mucousae
What are the layers of the mucosa of the gut wall?
Muscularis mucosae, lamina propria and epithelium
What are serous membranes?
Thin, two-part membranes which line closed body cavities (spaces that do not open to the exterior). They envelop the viscera.
What are the viscera?
Body organs
What is the serous membrane enveloping abdominal organs called?
Peritoneum
What is the serous membrane enveloping the lungs?
Pleural sacs - a pleura is a serous membrane which folds back onto itself to form a two-layered membranous pleural sac.
What is the serous membrane enveloping the heart?
Pericardium
What do serous membanes secrete?
A lubricating fluid which promotes relatively friction-free movement of the structures they surround
What does a serous membane consist of?
- Mesothelium (simple squamous epithelium) which secretes a lubricating fluid
- Thin layer of connective tissue which attaches the epithelium to adjacent tissues and carries blood vessels & nerves
What is the inner layer of the serous membrane called?
Visceral
What is the outer layer of the serous membrane called?
Parietal
What are epithelia that are one cell layer thick called?
Simple
What are epithelia that are more than one cell layer thick called?
Stratified
What is the basement membrane?
Thin, flexible, acellular layer which lies between epithelial cells and connective tissue
What does the basement membrane consist of?
Basal lamina which is laid down by the epithelial cells and therefore lies closest to them
What can the thickness of the basement membrane be augmented by?
A variably thick layer of reticular fibils (type III collagen), elaborated by the subtending connective tissue
What does the basement membrane serve as?
A strong, flexible layer to which epithelial cells adhere. It also serves as a cellular and molecular filter.
What is the simple squamous epithelium that lines the pleural sac, pericardial sac and peritoneum called?
Mesothelium
Where are simple squamous epithelia found?
- Endothelum of blood vessels and lymph vessels
- Alveoli
- Bowman’s capsule
- Loop of Henle
- Mesothelum of pericardium, pleura and pertonium
What are the functions of simple squamous epithelia?
Gas exchange (alveoli)
Barrier (Bowman’s capsule)
Lubrication (pericardium, pleura, peritoneum)
Active transport by pinocytosis (mesothelium + endothelium)
Where are simple cuboidal epithelia found?
- Thyroid follicles
- Small ducts of exocrine glands
- Kidney tubules
- Ovary surface
What are the functons of simple cuboidal epithelia?
- Absorption
- Secretion
- Barrier
- Hormone synthesis, storage and mobilisation
Where are simple columnar epithelia found?
- Stomach lining and gastric glands
- Small intestine and colon
- Gallbladder
- Large ducts of exocrine glands
- Oviducts
- Uterus
- Efferent ducts of testis
What are the functions of simple columnar epithelia?
- Absorption (small intestine, colon, gallbladder)
- Secretion (gastric glands)
- Lubrication (small intestine and colon)
- Transport (oviduct)
Where are pseudostratified epithelia found?
- Lining of nasal cavity
- Trachea
- Bronchi
- Epididymis and vas deferens
- Auditory tube
What are the functions of pseudostratified epithelia?
- Secretion and conduit (respiratory tract and vas deferens)
- Absorption (epididymis)
- Mucous secretion (respiratory tract)
- Particle trapping and removal (respiratory tract)
What are the epithelial cells in the vagina rich in and why?
Glycogen - it is a substrate for numerous lactobacilli which produce lactic acid and therefore maintain a low pH.
Where are stratified squamous non-keratinized epithelia found?
- Oral cavity
- Oesophagus
- Vagina
- Part of anal canal
- Inner surface of eyelid
- Larynx
- Surfact of cornea
What are the functions of stratified squamous non-keratinized epithelia?
- Protection against abrasion
- Reduces water loss but remains moist
Where is stratified squamous keratinized epithelium found?
Epidermis
What is the epidermis mainly made up of?
Keratinocytes and their products
What are the four layers of the epidermis?
Stratum corneum
Granular layer
Prickle cell layer
Basal layer
Where does keratinocyte mitosis occur?
Basal layer
What do keratinocytes synthesise?
Keratins which strengthen the epidermis and are the main constituents of hair and nail
What happens after keratinocyte mitosis in the basal layer?
Daughter keratinocytes move upwards to form the prickle cell layer where terminal differentiation begins and keratinocytes lose their ability to divide.
What happens to keratinocytes in the granular layer?
Keratinocytes lose their plasma membrane and begin differentiating into corneocytes.
What are keratohyalin granules?
Aggreations of keratins, fibrous proteins and enzymes (eg phospholipase) found in the granular layer
What is the stratum corneum made up of?
Layers of flattened corneocytes (major role in skin barrier function)
What is the transit time of a keratinocyte from basal laye to stratum corneum?
28-40 days
Other than keratinocytes, what other cells are found in the epidermis?
Melanocytes and Langerhans cells
What are melanocytes?
Dendritic cells that occur at intervals along the basal layer and produce melanin
Where do melanocytes originate?
Neural crest
What are Langerhans cells?
Dendritic cells scattered through the prickle cell layer that a capable of antigen presentation to T lymphocytes
Where do Langerhans cells originate?
Bone marrow
What are the functions of stratified squamous keratinized epithelia?
- Protection against abrasion/trauma
- Prevents water loss
- Shields against UV damage
- Prevents ingress of mirobes
What do transitional epithelium go from in an empty bladder to a full bladder?
From stratified cuboidal (empty bladder)
To stratified squamous (full bladder)
Where are transitional epithelia found?
- Renal calyces
- Ureters
- Bladder
- Urethra
What is the function of transitional epithelia?
Distensibility and protection of underlying tissue from toxic chemicals
What is a gland?
An epithelial cell or collection of cells specialised for secretion
How can glands be classified?
- By destination of secretion
- By structure of the gland
- By nature of the secretion
- By the method of discharge
What are exocrine glands?
Glands with ducts
What are endocrine glands?
Ductless glands which secrete into the bloodstream
How would you classify a goblet cell?
Unicellular exocrine gland
What are 3 methods of secretion?
Merocrine (exocytosis - vast majority of glands)
Apocrine (secreted droplets covered by plasmalemma eg fat droplets in milk)
Holocrine (whole cell breaks down - eg sebaceous gland of skin)
What are the 3 major salivary glands?
Parotid, submandibular and sublingual
Why is the pancreas an endocrine and exocrine gland?
Functioning as an exocrine gland, the pancreas excretes enzymes to break down the proteins, lipids, carbohydrates, and nucleic acids in food. Functioning as an endocrine gland, the pancreas secretes the hormones insulin and glucagon to control blood sugar levels throughout the day.
