Muscarinic antagonist
Suppresses salivary and bronchial secretions before surgery
Adrenaline
● Increased heart rate and leads to general vasoconstriction in the treatment of acute cardiac failure
Nicotinic antagonist
● Reduces the effects of sympathetic and parasympathetic nervous system → lethal
Beta 2 agonist
● Dilates bronchioles in the treatment of asthma without undesirably stimulating the heart
Beta 1 antagonist
● Selectively blocks beta 1 adrenergic receptors thereby reducing the sympathetic effects on the heart
● Reduces heart rate in the treatment of hypertension
Describe regulation of GIT functions
INVOLTUNARY
External stimulus (such as the sight, smell and taste of food) stimulates the central nervous system – LONG REFLEX
Internal stimuli (chemoreceptors, osmoreceptors, mechanoreceptors), can stimulate the central nervous system which affects the local nerve plexus, but can also directly stimulate the local nerve plexus through short reflexes. _ SHORT
SWALLOWING REFLEX
- Bolus is formed
- Brainstem closes the pharyngoesophageal sphincter so food doesn’t go up the nose
- Glottis closes so that food doesn’t go down the trachea
- Peristalsis pushes down the food
Sphincter of the stomach opens up due to mechanoreceptors
State the functions of the stomach
- Stores ingested food and begins digestion
- Secretes HCl and enzymes that begin protein digestion, also produces intrinsic factor
- Mixes food bolus and produces chyme
a. Mechanical digestion is break up of food particles
b. Chemical digestion
Describe how HCl is produced
● HCl is produced by parietal cells
● Secondary active transport brings Cl- from the plasma into the parietal cells
● Passive diffusion of Cl from parietal cell to the lumen
● Active transport of H+ from the parietal cell to the lumen
Describe the mechanisms that allow mucus to be a protective barrier
1. Impermeable mucosal cells ● Luminal membranes are impermeable to H+ 2. Tight junctions ● Prevent HCl from penetrating 3. Mucous coat ● Physical barrier to HCl 4. Chemical barrier ● HCO3- neutralizes HCl
*** Describe the regulation of gastric secretion
● Neural control: acetylcholine
○ Released by intrinsic nerve plexuses within the stomach under the control of short local reflexes and vagal stimulation
● Hormonal control
○ ECl cells: secrete histamine among the parietal and chief cells (oxyntic mucosa)
○ G Cells: secrete gastrin into the blood stream
○ D cells: secrete somatostatin in the response to the acid
The control of gastric secretion involves three phases
- Cephalic phase
● Factors arising before food reaches the stomach
● Stimulated by seeing, smelling, tasting, chewing food
● Activates the autonomic nervous system
● Acetylcholine is released and activates the chief cells, parietal cells, ECl and G cells - Gastric phase
● Factors result from food in the stomach
● Once food reaches the stomach
● G cells are activated by short reflexes and produce gastrin
● Gastrin is released into the bloodstream and activates chief cells, parietal cells and ECl cells
● More HCl is produced by the parietal cells and more pepsinogen is produced by chief cells once food reaches the stomach
● Histamine is produced and is final drive of the whole system → most important step - Intestinal phase
● Factors in the duodenum after food has left the stomach
● D cells sense the change in pH and produce somatostatin
