6. tissues and organs

Serosa Structure and function

Outer layer of connective tissue – provides a very thin protective and supportive lining

Muscularis externa Structure and function

Consists of an outer layer of longitutinal muscle – contraction causes pendular movement

And can inner layer of circular muscle – contraction causes local constrictions which causes peristaltic waves to help push food along.

Both muscle help churn and mix the food

Submucosa

Composed of connective tissue and many blood vessels and lymphatic vessels which transport absorbed food products

Muscularis mucosa

Thin layer of muscle. Important in moving the villi to increase contact with the food in the lumen. Small strands of muscle extend into each villus in the mucosa and contract to create a wafting motion.

Mucosa

Layer in contact with the food in gut lumen. Increased surface area due to the presence of villi and microvilli. Villi – finger like extensions of the muscoa layer Micovilli – extensions of the columnar epithelium

How do columnar epithelial cells have surface area extended

Prescient of numerous microvilli give brush border appearance

Why are the columnar epithelial cells rich in mitochondria?

Produces ATP for active transport of absorbed food molecules

Describe how the products are absorbed into the blood. E.g Glucose, amino acids, lipids.

Involves active transport and diffusion involving protein carrier molecules.

Glucose and amino acids are taken into the epithelial cells by active transport and then diffuse into the blood capillary network.

Products of fat digestion, fatty acids and glycerol are transported by lacteals which are part of the lymphatic system. Move by diffusion

How is pinocytosis involved?

e.g. in babies, antibodies can mass from breast milk into their blood.

Goblet cells location function

Within the columnar epithelial cells

Secrete mucus

Capillaries Location Function

Within the villi

Transport amino acids and glucose

Lacteal Location Function

Within the villi

Transport products of fat digestion/fatty acids and glycerol to lymphatic system

Crypts of LieberkÜhn Location Function

Intestinal glands that lie embedded in the tissue between villi

Cells continually divide to produce new cells that form the columnar epithelium

Paneth cells Location Function

Base of the crypts

Antimicrobial function in protecting their neighbouring actively dividing cells

leaf diagram

Upper epidermis

Protective layer – no chloroplasts. Covered by a waxy cuticle which prevents water loss and is transparent allowing light to pass through to PML

Palisade mesophyll

Photosynthesising layer. Regularly arranged and tightly packed = increase S.A.

Contains lots of chloroplasts to maximise light absorption for photosynthesis

Spongy mesophyll

Cells loosely and irregularly arranged – Increase S.A for gas exchange. Contain intercellular air spaces that encourage diffusion of gases. Do not photosynthesise

Vascular tissue

Xylem and Phloem.

Lower epidermis

Contains waxy cuticle – thinner than upper. Less transpiration occurs here.

Stomata

Pores. Close at night. Allow gases to enter or leave, including water vapour

Guard cells

Possess chloroplasts. Involved in opening and closing of stomata. When not turgid they close to prevent water loss