Lesson 4- Part II - Histology

Question 1

Describe the dermis [cutaneous]/[the second layer of the skin below the epidermidis]

Answer 1

-It is considered to be true skin
- separates epidermidis from hypodermis
-contains blood vessels and nerves
-dermal/epidermal junction connects the dermis to the epidermis 
-The dermis is about 25 times thicker than the epidermidis
-This connective tissue provides the framework that supports epithelium and other tissues
-it has an essential role in transportation, protection and repair
-this tissue contains matrix in which lie many collagenous, elastic and reticular fibres
-Rete ridges anchors the epidermidis to the dermis [shown in picture below]

Question 2

How many layers does the dermis contain [list them]

Answer 2

Two

• Papillary
•  reticular

Question 3

Describe the papillary layer of the dermis

Answer 3

• The most active layer of the dermis
• It connects the dermis to the epidermidis, forming the epidermal/dermal Junction
• The upward waves are fingerlike extensions of the dermis called dermal papillae
• Downward waves are extension of the epidermis called epidermal ridges
• Attached to dermal papillae are either looped capillaries that nourish the upper dermis or tactile corpuscles, the nerve endings sensitive to touch and pressure
• The papillary layer comprises 10 to 20% of the dermis
• Most of the connective tissue cells can be found here
• The papillary is important in the repair of all tissue
• Put Hillary projections into the epidermidis allow for more freedom of movement and delivery of nutrients to the epidermidis as it provides a larger surface area. Nerve endings move through the papilla for better pick up of sensation. Blood cells provide nutrition and fight against bacteria.

Question 4

Describe the reticular layer of the dermis

Answer 4

• It is 4/5 of the dermis
• Elements in this tissue are the same as the papillary layer but the collagen, elastin and reticular fibres are far denser and they mostly run parallel to the surface giving the skin strength, tone and elasticity
• Damage to these elastin fibres as they break down are the primary cause of sagging, wrinkles and ageing –loss of elasticity to the skin
• Stretch marks are caused by damaged elastin fibres
• collagen and elastin are broken down by UV damage and other factors

Question 5

Define collagen

Answer 5

Collagen is a proteins substance of complex fibres that gives skin its strength and is necessary for wound healing. Collagen is produced by fibroblast cells. These fibroblast cells help in production of collagen and elastin

Question 6

Define glycosaminoglycan [GAG]

Answer 6

• is a large protein molecule and water binding substance found between the fibres of the dermis.
• found between the collagen and elastin fibres
• GAG‘s are polysaccharides-protein and sugar complexes.

Question 7

Define elastin

Answer 7

Is the fibrous protein that forms elastic tissue and give skin elasticity

Question 8

List other fibres that can be found in the dermis

Answer 8

1. Fibroblasts [cell stimulators] they aid in the production of collagen and elastin by producing proteins. They make up 70% of the dermis.
2. Lymphocytes [fight infections]
3. Langerhans cells [guard cells]
4.  Mast cell [involved in allergic reactions]
5. Leukocytes [white blood cells to fight infections]

Also found in the dermis are blood vessels, nerves, sweat glands, oil glands, arrector pili muscles and hair Papilla. 

Question 9

Define hyaluronic acid

Answer 9

Hyaluronic acid is part of the dermal substance. Hyaluronic acid is a GAG. It delivers all substances to the cell and its stores H2O, salt, and glucose temporarily.

• hyaluronic acid is found between the fibres of the reticular layer
• it maintains water balance, aids in cell migration, metabolism and growth

Question 10

Describe the hypo dermis layer of the skin [subcutis or subcutaneous layer]

Answer 10

• This is connective adipose tissue in which many cells are filled with fat. This is called adipose tissue
• This layer is 80% fat, it’s stores food which may be oxidized bus producing energy.
• Reduces heat loss through the skin.
• It supports, protects and acts as a shock absorber around organs.
• Hormones influence fat storage
• vessels, nerves, fibers, adipose cells, fibroblasts and other cells are just some of the components of the hypodermis
• this layer decreases by age

Question 11

What are nerves [appendages of the skin]

Answer 11

The skin contains fine endings of nerve fibers, which pick up sensations and relay messages for the body. They are associated with pain and itching sensation, and their endings are closely situated in the epidermal tissue in the hairy areas of the body/skin.

Question 12

Nerves in the skin can be classified into how many different types? List them.

Answer 12

Three

1. Sensory
2. Motor
3.  Mixed

Question 13

Describe sensory or aefferent nerves.

Answer 13

Afferent - nerve fibres send messages to the central nervous system and brain to react to heat, cold, pain, pressure, touch and itching. Most of these endings are free nerve terminals that do not have a specialized ending. They are associated with pain and itching sensation, and their endings are closely situated to the epidermal tissue in the hairy areas of the skin. The skin must not only be able to sense pain etc. but also be able to distinguish degrees of the sensations that is light to heavy or fast to slow.

Question 14

How many different types of sensory nerve endings are there? List them.

Answer 14

Five

1. Meissner’s corpuscle [tactile]
2. Thermo receptors
   - end bulbs of Krause
   - corpuscles of Ruffini
3.  Hederiform Endings (ivy shaped)
4. Paccinian Corpuscle
5.  Hair follicle endings

Question 15

Describe the Meissner’s corpuscle

Answer 15

• Located closer to the surface of the skin
• Known as the touch corpuscle
• Located in dermal papillae of fingertips, Palm, eyelids, lips, tongue
• responsible for light touch sensations because it is located near the surface of the skin

Question 16

Describe thermoreceptors

Answer 16

• Closer to the reticular area of the dermis
• They detect both heat and cold
• besides the free nerve endings, there are two main types;

1. Corpuscles of Ruffini-are nerve endings in the subtitaneous tissue of the human finger and detect heat. They detect stretches of connective tissue and send slow, continuous signals when stimulated. The receptors nearest to the epidermal-dermal junction are Merkel‘s desk and Meissner‘s corpuscles. The paccinian corpuscles and the Ruffini corpuscles are in the dermis. They reach the middle of the dermis. They register heat, pressure and joint movement.
2.  end bulbs of Krause-are found in the skin, the conjunctive of the eye, the mucus membrane of the lips and tongue, the penis and the clitoris and the finger tips. They are true Thermoreceptors and detect cold.

Question 17

Describe Hederiform endings

Answer 17

They occur in the hair list, skin and also called Merkel‘s disks. Add the nerve endings approach the base of the epidermidis it expands into flattened leaves that lie close to the specialized cells near the epidermal/dermal junction. They are attached to the local keratinocytes by desmosomes. They are thought to be Mechanoreceptors for touch and other internal functions.

Question 18

Describe Paccinian corpuscle

Answer 18

They are found in the deep part of the dermis of the Palms and fingers near the bones, specifically in the fingertips, palm and souls as well as the lips, tongue and face. They are also found in the external genitalia and the breasts and are sensitive to light touch. Many internal organs also contain these corpuscel‘s. They share Mechanoreceptor responsibility with the three other skin organelles. They have special sensitivity to deep pressure and high frequency vibration, and they relay change of position of the arms and legs to the brain.

Question 19

Describe Hair follicle endings

Answer 19

Hair follicle endings are single fibres joined at the hair bulb and wrapped around the end of the hair in fine body hair. And other hairs the nerve is above the hair bulb circling the external route sheath.

Question 20

Describe Motor Nerves / secretory or efferent nerves.

Answer 20

• Relay messages from the brain and spinal cord to the muscles or glands
• These nerves work on voluntary and involuntary muscles to cause movement.
• secretary nerve fibres are motor nerves attached to sweat glands and control sea bum output to the surface of the skin.

Question 21

Describe mixed nerves

Answer 21

Nerve of mixed fibers: a nerve composed of both sensory (afferent) and motor fibers (efferent).

Question 22

Describe the sebaceous gland

Answer 22

• Sebum oil secretory gland
• Sebum creates the acid mantle on the skin which protects the skin against bacteria entry
• Sebaceous glands are larger on the face and scalp then on the rest of the body
• Keeps skin and hair soft and supple
• Located at the hair follicle and empties into the hair follicle
• it is very active during puberty

Question 23

Describe Sudoriferous glands

Answer 23

This gland helps to regulate body temperature and illuminate waste products by excreting sweat. They have a coil base and a duct opening to the surface known as pores. The excretion of sweat is controlled by the nervous system. Normally 1 to 2 pints of liquid containing salts are eliminated daily through sweat pores.

Question 24

Describe the two types of sudoriferous glands

Answer 24

Apocrine sweat gland

• It is confined mainly to the under arms, genitals, anal canal, areola, and in mature males, the beard area.
• They are sent glands that respond especially to stress and sexual stimulation
• They serve to produce pheromones, the chemical that influences the physiology or behaviours of other members of the species
• Produces alkaline secretions
• It becomes functional with puberty
• Odour associated with these glands is due to the interaction of the secretions and bacteria on the surface of the skin
• According to some authorities, apocrine glands are not true sweat glands because they’re opening connect to oil glands instead of poor openings directly to the skin surface
• it’s secretes into the hair follicle and not directly onto the surface of the skin

Eccrine Sweat Glands

• It is formed everywhere on the body primarily on the forehead, palms and soles
• These glands are not connected to hair follicles
• There are 3 to 4,000,000 of these in the adult skin
• They are more active when the body is subjected to physical activity and high temperatures
• On average, sweat is 99% water has a pH ranging from 4 to 6
• Eccrine sweat does not typically produce an offensive odour

Question 25

Describe hair characteristics

Answer 25

• It starts in the dermis where it originates
• Consists of the follicle, oil gland, muscle [arrector pili], and sometimes sweat glands
• Keratinized cells provide structure to the hair
• Melanocytes provide colour
• Arrector pili muscle provides thermal regulation
• Hormones control hair growth
• The free and we see above the surface is the hair shaft

Question 26

Describe the hair follicle

Answer 26

• Hairs are keratinized [made from keratin protein] structures produced by the hair follicle
• Follicle a slanted
• Sometimes more than one hair grows out of the follicle
• Hair contains 90% keratin and is a particularly tough, elastic material
• We have millions of hair follicles covering our body
• The base of the follicle surrounds the nourishment source for the matrix called the dermal papilla

Question 27

Structure of the skin pictures from student manual

Answer 27